Yeah, the old 2450/2500 is the bottom of the barrel now as far as processing power goes. But the old Roku 1 (2710) is only slightly better (in my tests) and there a bunch of them out in the wild, especially since they re-branded it "SE" and sold it for Black Friday for $25 a couple years back. Heck, even 2016's Express 3700/3710 is relatively weak, and only NOW are ALL Rokus on the market strong performers.
Maybe Fall 2017 could become the new cut-off point after a few more years, such as 2020/21. Then again, "older" players such as the Roku 3 4200 can still show a lot of muscle and wouldn't deserve to be included in a cut-off group, so I'm not sure how to best handle it other than a big specific list of supported vs "retired" model numbers.