I’m building a “new” high spec 26er, around a refurbed frame- I was planning to go bigwheel after the old frame cracked but I got a replacement triangle for it instead so refreshing the whole bike.
My prediction is that yes cool new stuff becomes scarce in 26, and over the next few years it’ll get harder to walk into a shop and buy things. But there’ll be stacks of used stuff as people switch to 650b, and sale stock, and it’ll still be possible to get what you want online- if maybe not precisely what you want.
The main thing is, the resale values of 26 inch parts are going to be lower… Pretty much zero I expect by the time I replace this bike. Personally I wouldn’t be buying a new 26er at the moment but I don’t mind dropping a fair wedge of cash on making my last 26er a bloody brilliant one, it’s still cheaper than the 29er frame I was going to buy. (probably a COvert, coincidentally!)
ymmv 😉