Summoner would be extremely difficult to do, since companion rules are pretty bare-bones right now. I'd probably just use the sorcerer as it is to represent a warlock in the 5e style, which...also works nothing like a summoner. The only thing I can think of is to let the warlock pick a list of summonable creatures as their "eidolon", and just reskin each higher level version of the creature as the "leveled up" version of the previous one.
To illustrate why a real summoner would be difficult, you'd basically need to create a bunch of base stats from scrach, and make them workable within the 10-class-feat paradigm. That is, each advancement would cost a class feat, as opposed to the fairly exploitable evolution point mechanic from 1e.
I can't imagine the amount of work that would go into homebrewing the base stats for an outsider for each of 9 planar alignment, plus genies, elementals, fey, shadow plane denizens, aberrations, undead, and golems. That's a whopping 16 base types, and each needs at least two feats per level. Assuming most feats can be shared between multiple types (all fiends, all celestials, between genies and elementals, etc), you're still looking at something like 100 feats to write.
Good luck if you're willing to start on the endeavor, but I wouldn't bother at this point.
I would take a page from the later 4e summons.
Mainly, each creature had a set of rules to follow.
Most animals would just "move to the closest enemy and then attack". But wolf's would move into flanking.
Demons would attack the nearest anything and could not be dismissed.
Elementals would act more like hazardous terrain, flinging AoEs all over.
And I think the unicorn was "heal the nearest bloody (below 1/2 health) ally first. Otherwise attack"
That way, each came with a personality, and turns go faster as they just go.