What differentiates a wayshifter from other mages is the specialty. Traveling reliably between worlds and to specific locations requires a high degree of knowledge and skill. Wayshifting could take decades to master, and the best wayshifters were always in high demand. With such a high degree of specialization, it's a wonder it never became known as a "-Mancy" the way other forms did. Perhaps it is because, unlike other 'mancers, wayshifters were typically powerful general-purpose mages in addition to their specializations.
During the Mage Wars, Wayshifters were usually not allied with any power, and tended to operate as independents, mercenaries of a sort. Wayshifter spies were a common problem during the Dynastic Period. Wayshifter guilds were well known, and it was often said a Wayshifter's only loyalty was to their guild, "if that".
The first dedicated Wayshifters arose in the First Chaotic Period as inter-dimensional trade began. They were also commonly employed to help refugees escape, though by the mid period it was clear nowhere would be safe. Prior to the rise of Wayshifting as a dedicated practice, there were many mages who found ways to travel between worlds, as testified by the existence of the Waystone Network.
By the late part of the First Chaotic Period, Wayshifter guilds could be found in every city. These were close-knit, tightly organized groups where extremely secretive. Most guilds required tattoos or other permanent markings as identifiers, and associating with any guild other than one's own could mean death. This was due to the important techniques and secrets each guild held, which was its only economic leverage over the others.
During the Intermediate Period while other guild organizations began to ally themselves with government powers, most Wayshifter guilds instead went underground. Their guild halls, the real ones, anyway, were moved to secretive locations off-world known only to guild members. This allowed guilds to begin branching out, setting up offices in multiple cities--sometimes across warring empires.
The art became increasingly mistrusted as the Dynastic Period began. Wayshifters developed a reputation for being untrustworthy, greedy, and generally bad people. How much of that is true remains in question, but it is known that the various guilds devolved into cult-like fanaticism.
In the Dynastic era, most major powers had specialized court mages whom they could trust (primarily using the Phase-shift method, and developed networks of their own. Wayshifters remained common for trade and were important as guides. A good generalist mage could master phase-shifting but would not know destinations. Wayshifters who would not willingly provide imperial powers with access to new worlds to conquer were often tortured quite brutally.
In the Second Chaotic Period, wayshifting regained some of its glory, as wayshifters formed an integral part dismantling the empires. Wayshifters finally took sides, mostly the side of freedom, and many were willing to join the ranks of Eieber. As a critical part of his war effort, he had a knack for inspiring loyalty. One old wayshifter recounted this had more to due with his promise of peace than anything else; the guilds, at least any he knew of, had no interest in conquest, and merely wanted to practice their trade. Of course, many wayshifters did become quite wealthy during this era.
During the early part of the Golden Age, wayshifting flourished; but the writing was on the wall. The GATE network was under construction, and by the end of the first century was already able to provide most of the major routes linking important cities and economic networks. Wayshifters also found their trade in much lower demand as the need for inter-dimensional trade had dropped substantially. Whereas before the primary driving force was the search for rare alchemical and enchanting materials, modern trade consisted more heavily of bulk mundane goods, a market the Wayshifters could not easily be involved in. Further, exploitation of resources on home dimensions led to a drop in over-all inter-world trade.
In the second century of the Golden Age, Wayshifting saw a brief resurgence as a boutique travel service. Inter-world commerce was still happening even if it was lessened, and a good wayshifter could offer door-to-door service. With the GATE network still in its infancy, a business man may have to travel for several days or even weeks to reach a hub, or be forced to live in a city close by. Wayshifters could come to you, take you directly where you needed to go, and bring you back again. However, the price of their services was expensive, and the new economy called for much greater specificity in destinations. For the price, travelers often expected to be taken directly to the room they were destined for, not merely the street outside or even just the city.
In the later part of the century, the shift came again to that of an "adventure travel service". Catering initially to the very wealthy, a wayshifter could come to your house, transport you and your family to an exotic, far-off destination, help you explore for a few hours, and then bring you back safe and sound. However, when that last part failed to happen on a few high-profile occasions, the old mistrust and prejudices came back.
A few wayshifters slashed their fees and began competing for the less lucrative but less litigious middle-class market, focusing on bringing travelers to far-off-but-still-populated locals, and catering more as a pick-up/drop-off than as guides. This in turn led to more high-profile disasters, and within a generation the number of wayshifters fell considerably.
By the mid Golden Age, the GATE system had almost fully superceded the need for shifters. A few guilds, mostly generational families at this point, remained in practice. Their chief niche role was the ability to quickly take people out of large cities and get them to nature if they felt so inclined. Often times the wayshifters themselves would live in houses they'd built in remote, unpeopled places, and maintain a sort of office or frontage in an expensive part of a major city. Clients would then be transported to their home where some amenities existed amidst endless miles of trackless wilderness. This practice, while successful, was ultimately the death-knell for wayshifting, as practitioners no longer needed the ability to navigate or to know many places, they simply had to travel between two.
When the GATE network became fully functional and offered a slightly less convenient but much cheaper service, the last wayshifters fell completely out of fashion. Their one ability, the power to take you anywhere, had been lost centuries ago, and of the few that remained many were now merely phase-shifters, operating ritual sites with no knowledge of how they worked or how to go other places. By the end of the Golden Age, the practice had died out entirely.