Several megas are different enough they should have been regular evolutions, especially on pokemon lacking a full evolution line like houndoom or pinsir. Also a few gigantamax forms like orbeetle and sandaconda look like they complete the line more than are meant to be the same pokemon with a power boost so when that gimmick gets tossed they'll feel really incomplete. Some general lines that could use another stage in my opinion: rapidash -> pegasus and/or sleipnir inspired evolution fire/fairy because mythological great steeds and it's an unused type combination, garbodor -> dumpster, baby single headed fluffball -> doduo.
