Hi Stefan,
Well, that would be a question to some sales people or SEs...
I still see 7522 in the pricefile so I bet they will go EoS much sooner. 7632 should be on sale for at least next several years, entire 76xx is kind of a flagship model family right now since not that long.
Extreme seems to be aware that 11ax is not that must-have-asap as the market seems to consider it. Many years will pass before you will benefit 11ax, but yeah, new chipsets and features though.
I'd leave it up to you. It would be needed to check if with WiNG 7.x a 75xx family is going to be supported. If yes, you're good to go with buying 7522 to enhance your impressive 1.5k collection. If not, having only 7522s would put you in need to migrate bigger amount of APs (if you are really interested in moving to WiNG 7.x and AP300s)...
Personally I didn't hear Extreme staff discouraging from buying 7632s.
Hope that helps,
Tomasz