Certain popular AMD SKUS are already 120 days lead time and growing. If a vendor will talk to you at all.
I expect motherboards to get cheap until they get to be really expensive niche products should the current situation last a few more years. At least as we know them today as PC enthusiasts and/or prosumers. I could very much see that market evaporating entirely and moving towards large integrators instead. Gamers and such were already a rather small niche to begin with.
Right now the saving grace is a server board doesn’t look a whole lot different than a consumer board. But that may change significantly faster than anyone predicts should current trends with SoCs and the like continue. You may be in a place soon where you get to choose your CPU/RAM/storage at purchase time like you do with a MacBook today.