To me it is a concern because I don't like games that tend toward wood-chopping. Positional aspects must be strengthened. The super-knights are very technical, anti-positional, pieces. In this environment one should retain every positional aspect possible. I haven't tested your IAGO chess although you sent me the zrf because I have been so busy. It would be easy for you to prohibit simultaneous gating of the Hawk and bishop movement, however. I am sceptical of free introduction of pieces, i.e., that the player can wait as long as he wants. Generally, a game must have restrictions so that strategical problems are created for the players. There ought to be a strong current in the game toward resolution. If he can wait as long as he wants with the introduction of a heavy piece, then an immensely strong defensive force is always in prepare, while he can introduce it on so many squares. Thus, no matter how good the opponent plays positinally, he cannot achieve a strategically won game. He can only win tactically, and then the game is lopsided towards the tactical. (I know I really shouldn't criticize your variant without having tested it, but here it seems so obvious). 

I have introduced another method in Alternative Chess: 
http://hem.passagen.se/melki9/alternativechess.htm
In this variant one can also choose to have both the super-knights as extra pieces, but introducing them is compelled, while one must do it on the second rank where a pawn is situated. Introduction can only occur simultaneously with a pawn moving two steps. It is strategically very dangerous to wait, because introduction will weaken your pawn chain drastically, especially if you introduce the piece on g2/g7, for instance. In this way the game has a strong current in that the pawn's double-step creates an aggressive game and also weakens the pawn chain. While the opening proceeds, the squares (unmoved pawns) where the extra pieces can be introduced become fewer and fewer. Soon the opponent can predict where the piece must be introduced and can take preventive measures. In this way, introduction of external pieces becomes a positional and strategical problem. One must alsways strive, I think, to create a problematic game, because chess players want to grapple with problems. 

It's no wonder that Chinese Chess is the world's most popular game. The problems start immediately in the opening. Three of five pawns are unguarded and are soon attacked, big problems concerning the development of pieces starts immediately. If the rook isn't activated in three moves it is said that the game is lost (but thats an exaggeration). There is no time to wait. Should one have an extra powerful piece to insert at any time, in the endgame even, then Chinese Chess would have been defunct, because then the player can solve his problems in a stroke. So I am sceptical about delayed introduction on any empty first rank(?) square.

Mats