Here's an important distinction for TUGgers: the relationship change with RCI only applies to WELK PLATINUM members (as distinguished from RCI PLATINUM members.)
Current owners of Welk properties who are outside Welk's Platinum Points System are unaffected--as are their RCI WEEKS or RCI POINTS memberships and/or their exchange options with RCI and II.
(I only know about their Escondido resorts firsthand--have been vacationing there since the 1980s--but this distinction seems likely to apply to all previous Welk owners worldwide who have not "upgraded" [converted over] to the Welk Platinum system.)
So RCI POINTS owners can still trade into the OLD "Villas" properties as well as Villas on the Greens (NOT Mountainside resorts when last I checked), as can RCI WEEKS members and II members. Welk management has touted its OWN "new" PLATINUM ownership (their own, private internal points exchange system, not to be confused with RCI PLATINUM memberships, RCI POINTS, or other systems’ points memberships.) Naturally, maintenance fees are higher if "old" LW Resort Villas or Villas on the Greens owners “upgrade”/convert to the Welk Platinum points system, and I would only suggest doing so after checking the internal exchange options and TUGger experiences of actually trying to trade their Welk Platinum points for other desirable resort destinations in the new exchange network.
(Such a costly upgrade might become more attractive for internal exchange once the current ambitious Welk construction projects, e.g., Breckinridge and Hawaii, are completed in the coming years, however.)
Meanwhile, outside of TUG Timeshare Marketplace listings, all sorts of Welk purchasing, renting, (and listing without cost via brokering) options can be found through calresale.com, (a full-service realty site which I purchased from, circa 1985, and is now operated by the website founder's daughter.)