Originally the concept plan for FPSC was for a world size of 100 x 100 tiles which was it seems a little over optimistic and so we have a world size of 40 x 40 tiles.
The reasons are many and varied and have been discussed in great depth and well documented in great detail over many years.
Aspirations of users and TGC perhaps for a larger world size have been of necessity tempered by the reality of the product and its development. TGC in the product development and users in practical application for development of game levels.
Quite major improvements to the core engine would be needed to facilitate a larger world size capability without further impacting on engine performance and end user gameplay and to simply enlarge the world size would be counter productive overall in the wider aspect of game making with it.
If Lee could have given you a larger world size then no doubt you would already have it after all these years.
All or most of the issues which prevent that still exist as far as I am aware so its unlikely that you will get it at least for the moment.
Given that the engine capability and performance is improved enough perhaps by the migration development work and beyond, then if frame rates hold up substantially in levels where the current world size is fully utilised without major performance hit issues then that will at least be a stable base to consider further improvements and possibilities.
Without stability of the engines performance and other core pre-requisites in place I don't see Lee making his and everyone elses job harder by simply increasing the world size.
The burden of AI, Polygon counts, Portal rendering, Zoneing, LOD, engine and user game level optimisation are just some of the issues needing to be considered and both the TGC and the end user would have to do a great deal of work to get FPSC to perform adequately utilising a larger world size.
Thus far recent speed improvements to the engine are encouraging, however issues and instabilities still exist and they hold back FPSC and always have done so.
Wait for the Migration and see what you get. Hopefully at least the AI drain and a few other issues will settle down and you will be half way there.
At the moment there are two versions of FPSC and a large number of endless engine Mods all in a state of heavy development and fluctuation.
Lee is a clever guy and will be aware of what increasing the world size will mean to end users because he will have tested out FPSC with an increased world size to see how it holds up. You should trust Lee and his assessment must be that its not a good idea or you would have it.
Outdoor levels, large terrains, 100 x 100 tiles world size all very desirable but at this moment I would suggest if you were given it you would be sorry - your game unless largely devoid of content would grind to a halt.
100 x 100 tiles in FPSC would be just a user nightmare at the moment in my opinion and I am an ardent supporter of larger world size for FPSC. Most of my levels indoor and out in fact take up the whole of the FPSC world.