1. c4 repertoire?

ah yes I forgot about 1...b6 or 1...g6 they are indeed good flexible alternatives rarely seen

1...e6 can transpose into the French or along with 1...nf6 or 1..b6 can transpose into the queens indian defence here in the queens indian playing e4 with keeping the anglo-queens indian with d3 not d4 means a line such as 1 d4 Nf6, 2 c4 b6, 3nc3 bb7,4 e4 e6, 5 nf3 bb4 isn't as uncomftable for the e pawn as in the anglo-queens indian this goes 1 c4 nf6, 2 nc3 b6, 3 e4 bb7, 4 d3 e6, when 5 nf3 is perfectly playable as the e4 pawn isn't embarrassed by the bb4 pin as it is doubly defended.

as can be seen by blacks many opportunities to play 1e4, or 1d4 openings in his pet opening system, it is black who can often decide the direction of the game but very often playing d3 instead of d4 can be employed to keep the game an English opening with less travelled paths.

another line to aim for as white is the botvinnik system which goes 1 c4 2 nc3 3 e4 4 g3 5 bg2 6 nge2 7 d3 as moves for white- as with all things botvinnik it is a very good system with f4 or b4 being pushed by white depending on opponent and tastes.

in the 1 ... e5 line i prefer setups with ... Bb4 and, if possible ... c6 and ... d5. The reversed Dragon setups are difficult to play for black if white is well prepared and even if black neutralizes white, he often has not more than boring draws. At least that is my experience with black.

I also sometimes play setups with ... g6, ... c6, ... d5 and later maybe ...b6 and ... Bb7 and when im done with development i prepare ... e5 or ... c5.

1... e5 is probably better (white has less choices), but ... g6, ... b6 is more flexible as @Sarg0n already said.

I would be careful with Botvinnik, there are crtitical lines like (the pawn sac)

1. c4 Nf6 2. Nc3 c5 3. e4 Nc6 4. g3 e6 5. Bg2 d5 6. exd5 exd5 7. cxd5 Nb4

1. c4 Nf6 2. Nc3 c5 3. e4 Nc6 4. g3 e6 5. Bg2 d5 6. exd5 exd5 7. Nxd5 Nxd5
8.Bxd5 Nb4

are close to refutations.

@no_bullet_thanks try playing the reversed Sicilian dragon with opposite side castling(ie black on the queenside castling), the attacks black can get are awesome and white is often struggling like in the Sicilian dragon proper.
as to 1...g6 or 1...b6 I always have mixed feelings because It is either a masterly move by a great player that knows what he is doing or it is a complete patzer surrender of the centre by a nonce that doesn't know what he is doing.

@Sarg0n once the black dark squared bishop cant go to the c5 square ie which it cant after 2...c5 in those anti-botvinnik system lines I always aim for the clamp with an almost immediate f4 and closing of the centre sure this two can be upset by a d5 push but it is less critical

@cap78red it would be nice if that was possible but if white plays for d3-d4 (like in the Dragon pawn sac variation) black doesnt have the time for preparing 0-0-0.

the most common lines for white don't involve d3-d4 as far as I know the main line involves targeting the c5 square for control by white I thought.