EnzomerSimpsons has been making Mane Six fusions recently, with some designs that I rather like. 8 so far, don't know if he's going to do the other 7...

6053283
Idea Applejack and rainbow dash = Zap Apple

6053283
What we have
A.J. & Rarity
A.J. & F.S.
T.S. & F.S.
T.S. & R.D.
P.P. & R.D.
P.P. & Rarity
F.S. & Rarity
F.S. & R.D.

So..
4 F.S.
3 R.D.
3 Rarity
2 T.S.
2 P.P.
2 A.J.

What we don't have
P.P. & F.S.
P.P. & A.J.
R.D. & A.J.
R.D. & Rarity
T.S. & Rarity
T.S. & A.J.
T.S. & P.P.

so..
1 F.S.
2 R.D.
2 Rarity
3 T.S.
3 P.P.
3 A.J.

Edit:
What we have
A.J. & Rarity
A.J. & F.S.
T.S. & F.S.
T.S. & R.D.
P.P. & R.D.
P.P. & F.S.
P.P. & T.S. 
P.P. & Rarity
F.S. & Rarity
F.S. & R.D.
A.J. & R.D.

So..
5 F.S.
4 P.P.
4 R.D.
3 Rarity
3 A.J.
3 T.S.

What we don't have
P.P. & A.J.
T.S. & A.J.
T.S. & Rarity
R.D. & Rarity

so..
0 F.S.
1 P.P.
1 R.D.
2 Rarity
2 A.J.
2 T.S.

6053351
Turns out you were right :)

6056043
The show set it up when zap Apple's where rainbows

6053283
Wow, these are really pretty!!

6060690
Indeed! I love some of the color choices :)

I somehow missed this (even though I had been waiting for it): the final fusion that Enzomer did. Unfortunately, he's since dropped this project, so this will be the last one.