New Species
Short of some ridiculous kind of fire stone evolution on an already Sun-stoned pokemon (Sunflora), Using a New Evolution just limits your movepool options too greatly. You can't just barge in, say "Ditto is now evolving," and then randomly throw in Body Slam, Ice Beam, and Force Palm into its learnset.
New Evos, especially of the kind we're implementing, are either unfounded (evolving a Stone evolution) or too llimited.
Sorry guys, but Sunflora already used a Stone Evolution. It's pretty much done unless you want to violate every precedent set in pokemon.
That and your "fast sweeper" ideas are pretty much blown out of the water if you use Sunflora as a base. Sunflora isn't just going to gain 75 Base Speed because its petals are now on fire.