Comments/Ratings for a Single Item

I do think that pieces like the Perier Cannon could be very interesting pieces to create a modest variant. But I am still skeptical about the gating mechanism you propose in this variant to introduce them. It introduces a second unusual complication. You mention yourself that it is a difficult strategic decision when to introduce the Cannon.

Wouldn't it be much simpler to start the Cannon, say, on b1, moving the Knight to a2, and the a-Pawn to a3?

Muller, to force a weakness in the pawn chain, and to have this as a criterion for piece introduction, is a good idea while the piece is introduced at a cost, making it strategically a relevant event, and it prevents the player from keeping the piece in reserve, which would give him undue defensive capabilities. For instance, depending on the powers of the external piece, it would be nearly impossible to succeed in an attack on the enemy king, while the defender couild simply insert the defensive piece at a suitable square. One cannot allow the player to delay the introduction of the piece while that would destroy the natural strategical flow of the game. In Burmese Chess, for instance, all pieces must be introduced before play begins. Otherwise, it wouldn't work strategically. In order to understand such aspects one must probably have a deeper understanding of chess resulting from serious study. Seirawan Chess only allows introduction of an external piece when a piece leaves the start square. In this way introduction follows naturally from the flow  of the game, and the player cannot keep an Elephant in the 'pocket' and introduce it whenever it suits him. This would be awkward and it would be impossible to lay out a strategical plan because you wouldn't know when and where the enemy external piece would appear on the board. So that's what's behind the gating principle in Seirawan Chess and in my variants. The reason why Seirawan introduced this rule is because he understands the principles behind chess.
/Mats

You are 'barking up the wrong tree', as I already completely agreed with what you say here. Unrestricted drops have an enormous impact on the entire game.

But this was not the alternative I was proposing: I wanted to get rid of the drop/gating altogether, by simply putting the exo-piece in a fixed place in the opening array. If I try to look at (many of) your variants through the eyes of a normal Chess player, I perceive this concept of gating as the most important new feature, not the fact that there is a new piece type. Games where it was possible to gate in a piece I already knew, say an extra Bishop, would already scare me off. The reason is that this type of gating must occur early, or you run the risk of losing the right to introduce the piece. So it will be an alien element, complicating opening theory. Normal Chess players rely very much on opening theory, and the idea that they might easily give away the game by not handling the introduction of the exo-piece correctly, while they have no idea how it should be done, could be a severe deterrent.

This is much less of a problem when the exo-piece starts in a fixed location, which is the same for both sides.