Well I'd hope so. And well, I'd think they'd play more like a mix between Ness/Lucas and Marth/Roy/Ike honestly. I could do a quick moveset (would probably work for either)
B: Ragnarok. Isaac / Matthew charge up their blade similary in fashion like the FE characters would (but with no freedom of letting go like them) and casts a huge sword-like projectile out of it about a Bowser and a half wide (with an awesome sweetspot in the very middle) about 2 characters in front of him. The move would be as slow almost as Ganondorf's Warlock Punch, but has around the same knockback (weaker still) and does a whopping 28~32% when sweetspotted. 19~22% if a little off, 10~14% at the very end of the move). The move would probably have some super armor as well at the last few frames of the move.
Up B: Growth. Plants grow out of the ground to attack, or grow around a ledge for Isaac to climb back to the stage (working similary to a ladder). The plants would cause a slight sort of trapping effect, and do around 5% damage, but could be a good set up for a stronger attack. The higher the other character's %, the longer they stay trapped kinda similar to how ZZS's stun works, but this one is somewhat weaker. You can escape the plants by jumping.
Side B: I'd want to put Move here, but I kinda dislike the idea of it being an attack for him so... I say this should be Stone Spire, a ranged charge up move involving stone spires falling out of the sky on an opponent. If charged for a little, just one Spire comes out, and does about 12~14% damage, and could be considered as Isaac's main projectile, as it'd be coming out as fast as PK Fire would (except it being slightly stronger and with shorter range). Charged up somewhat longer and Isaac would cast 2 Spires next to each other, each doing about 12~14% damage. Charged up fully Isaac would cast a total of 4 Spires, and the effect would be similar to Charizard's Rock Smash on earlier %s, and would have nice knockback.
Down B: Gaia. A moveable projectile you can aim at the ground, where you can create an earthy erruption out of when releasing B. Like Stone Spire, you can actually build up damage as well when holding B, but this one lacks the sheer power you can build up with Stone Spire, but it can trap better, and requires a little more skill even. It's a option only usable on SOLID ground, so not on small platforms, it can also be done around edges, but not OVER the edges as it needs ground to be preformed. And it's strongest or most effective when a character is on the ground as well. It's actually like a moveable mine of sorts, and can be as strong depending on how long you hold B. It's the same kind of story with Stone Spire, hold B briefly and release and Gaia would be a small erruption, covering about 1.5 a Mario wide and does 11~14% if the opponent gets trapped in fully. Hold it longer and you'd have Mother Gaia which'd already cover 3 Mario's wide and could do 16~18%, hold if for the longest and you have Grand Gaia, which is a massive attack doing 23~27% and delivers great knockback if the opponents gets trapped in the move fully. As a general rule with this move, the stones comming out of the erruption do the building up damage, would work KIND OF similar to the Smart Bombs.
General playstyle of Isaac would be harder to learn than most characters, as his ranged attacks are his biggest assets. His Psynergy is rather slow, but are very good setups, a small Gaia spell could be cast into a stronger Spire spell, or otherwise. He'd be highly unpredictable, but at the same time, rather slow and furnable while casting spells. He wouldn't like projectile spam himself either, but Isaac has a strong big shield to protect himself with (like, Mewtwo's big shield but slightly smaller) and a normal Spire would be fast enough to counter back with most of the time.
He's highly versitale in his B moves, and his A moves would mostly consist of sword attacks. His sword would be a little longer than Toon Link's, and are mostly swift attacks with only a few moves you can effectively kill with. As a Venus Adept he fights the best on the ground, and would perhaps have a below average aerial game and jumps. He also would be a tad lighter than Marth, but shorter as well. He would mainly be good at egdeguarding, and KOing characters from the side of the screen, not from the top. His grab game is above average though and his throws go far and do good damage, and could possibly be ranged if they implenent the Move ability from him in it (it wouldn't go as far as in Brawl, but rather about a character in front of him) to counter these seeminly broken grabs, if Isaac would miss a grab, there is some serious lag involved. His running speed is about as fast as Luigi's, maybe a little faster even. Overall he's a character you have to play with smarts, but he can be highly effective if used well. His Psynergy is powerful and great for setting up combos, but he's still rather fragile, and even though he has some speed you have to watch out for lag often.
EDIT: As a Final Smash, it must be Judgement:
http://www.youtube.com/watch?v=_iHwgkwtMUY
