I've been wondering a similar thing for how to take advantage of the 150k - 250k hardware routes the CRS317 now has in
v7 beta. That many routes should cover the peering tables for most operators, maybe even transit's customers.
Perhaps the thing you are looking for is SIR - the SDN Internet Router
GitHub - dbarrosop/sir: SDN Internet Router
TLDR; use pmacct to grab top N ASN speakers and install them into the FIB. Rinse and repeat.
Alternatively filter out anything not from ARIN. Conveniently fits into 250k:
Prefixes being announced by ARIN Region ASes: 238331
Cisco and Mikrotik BGP Filter For North American Routes | Greg Sowell Saves The World
Should you want something that isn't quite so bleeding edge beta, perhaps pick up a used Arista 7050QX? It's about the same as a CRS317 and holds 144k routes.