This is of course interesting, but this game will be too different from the German version of 4pс, which we play, and your version will require a separate site, the board is very huge, you will have to buy a widescreen monitor for it and the games will last a very long time.
In my opinion, it would be interesting to implement the Russian version of 4pc: https://en.wikipedia.org/wiki/Fortress_chess. 
Perhaps the fortress can be reduced from 4x4 to 3x3. Or simply on the board for the German version, open 3x3 cells in the corners and put up barriers.
I read about 2 Player Tamerlane Chess hear
https://en.wikipedia.org/wiki/Tamerlane_chess
and watched these videos on 2 Player Tamerlane Chess
https://www.youtube.com/watch?v=eekErvVYZLg
https://www.youtube.com/watch?v=SMUbX4vJseg
https://www.youtube.com/watch?v=WRdUfTVKJBA&t=1s
https://www.youtube.com/watch?v=udXtyd8mb6M&t=230s
They mention that moving into an enemy citadel is possible even if it's technically guarded by an enemy piece.
This is my idea for what a 4 Player Tamerlane Chess board could look like.
I was thinking that since in 2 Player Tamerlane Chess, who goes first is determined by the roll of a dice, that the default could be for who goes first to be determined using a random number generator, with players able to adjust who goes first when creating a new game.
The E represents the Elephant, the C represents the Camel, the D represents the Dabbaba, the R represents the Rook, the N represents the Knight, the T reprensent the Tali'a, the G represents the Giraffe, the F represents the Ferz, the K represents the King, and the V represents the Vizir.
The lowercase letters represent the pawns of each type of piece, with the pawn of each piece being represented by a lowercase letter that corresponds to the uppercase letter that represents each type of piece. The p represents the pawn of pawns.
Also the 4 extra squares are the default citadels.
I was thinking that for team games you should be required to get your king into one of the enemy citadels to declare a draw, with a player only being able to get the adventitious king into ones own citadel, or the citadel of ones own teammate.
I watched this video on the values of the pieces in Tamerlane Chess
https://www.youtube.com/watch?v=WA-p3OO-bRs
In summary it gives the following value to each piece
Rook=5
Dabbaba=1.45
Vizir=1.65
Knight=2.6
Camel=2.3
Giraffe=2.25
Ferz=1.5
Elephant=1.15
Tali'a=1.2
I was thinking that in FFA and Solo Tamerlane Chess that if a player gets his/her king into an enemy citadel, he/she could declare the game to be over, with all the remaining players, including the one who got his/her king in an enemy citadel, getting no more points than they would get after the game ending from the 50 move rule, or 3 fold repetition in standard 4 player chess.
I was also thinking that because stalemating the enemy king is a win in 2 Player Tamerlane Chess it could be set up so that when you stalemate an opponent, in FFA or Solo, you get the same number of points as you would from checkmating that opponent, with the players army dying as soon as he/she is stalemated.
I was thinking that for the 4 Player Tamerlane Chess Board Editor it could be the case that a player could edit, where the citadels are to be located, as well as choosing whether or not each player has the ability to swap the location of his/her king with a friendly piece.