I think is will breath fresh air into WvW and its always nice to see major attention given to the game mode.
My only concern is for players who play WvW regularly or as their only game mode but can not commit to guilds due to real life commitments or can not play at primetime (which most WvW guilds require) or are on the night cap team or roamers. A lot players are hardcore and only play WvW but are solo guild (bank) players or small groups/guilds that join tag/TS/Discord and would like to stick with the community they are with at present because it suits their needs. The alliance system looks like this would solve the problem and keep communities together as long as its not too strict and its flexible for the amount of guilds that can alliance.
An example would be guild A 50 players, guild B 30 players, guild C 20 players, guild D 15 players, guild E 5 players, guild F 2 players, guild G-Z 1 player. If the example is possible, flexibility with guild amounts in the alliance system to allow many guilds of lower number or solo hardcore WvW players to alliance with each other, I can see the system could work. The example above will keep communities together and players that regularly play together but not necessarily in one of the main WvW server guilds, if you see my point. If not then a lot of hardcore WvW solo guild players, small groups/guilds and roamers who join the community TS/Discord and join tag will be screwed and we will end of with communities we don't know, are not friendly with, not committed to and may eventually stop playing with for 8 weeks because we will end up stuck in a rut.
You could maybe argue the point to transfer to the alliance/community with the players you want to play with for 8 weeks but again there is limitations on that with population being fulls etc and paying to transfer will be forced onto players in this situation that has already been forced into the previous situation mentioned above. Players who get screwed will be double screwed with a pay wall every 8 weeks ££££$$$$$.