I have an amazing idea (I think)
Basically the idea is URPG War. All of the members are split into the five (six if we want Orange Islands) regions and each city is controlled by its gym leader, with people flocking to whichever city they want. The gym cities fight for territorry (including non-gym towns and cities) via FFAs (with fixed teams) with each trainer having more than one mon each if they want (and a maximum of six unless their defending). Each region has an income and special "abilities" and Pokemon, i.e. Goldenrod would get a free Bug-type every turn due to the National Park, Azelea would get extra income from Apricots etc. Once the regions are controlled by one city inter-regions begin, with places like Sinnoh and Hoenn having to use Water type "ships" to get to other places. Prizes are given based on FFA results, team for the city and the region.
Here's an idea of an FFA for Floraroma.
Three teams: Eterna (invaders) Jubilife (invaders) Floraroma (defenders)
Eterna has four trainers with eighteen Pokemon.
Oreburgh has three trainers with twelve Pokemon.
Floraroma has six trainers with Twenty five Pokemon.
Eterna trainer's can't attack Eterna Trainers etc.
The winner gets Floraroma along with the inhabitants (and some money from Plunder mwahahahahaha)