After reading through all 9 pages of feeds, my intense interest in said engine has almost flat-lined.
To bluntly answer your question, no. I do not believe focusing any direct development solely on adding Flight Sim capabilities at the cost of content.
Now to explain why. For a typical game developer, I look at an engine and ask a very simple question. What can I do with you. A game engine is a set of tools with a baseline kit, and the fundamentals to make game creation faster. The terms I'm hearing thrown about such as 'loading a flight sim mod' and such just baffles me, and not in a good way. That isn't to say that having a flight sim option would be undesirable.
In my honest opinion, some of these Flight Sim groups are interested in the availability of designing their physics into your game engine, and are curious of the potentials and limitations. This goes with the mindset of the most noble of questions that I think has been blurred since I first took interest in the Outerra Engine. Can I compile a stand-alone version from your engine for a playable game I can then distribute (with licence) via selling, or free releases. This comes with the additional comment. A game engine should be focusing on the fundamentals, and pre-packed with samples, tools, and guides to help a developer (me) understand what can realistically be done in the name of a game, and how to do it. Is this vision accurate to what you are implementing, or is your game engine simply going to be a 3D world editing environment specifically for use in your upcoming game.
Now that that's out of the way, if you answer "Yes, you can compile stand-alone versions", I can immediately suggest that you start implementing plugin/scripting 'hooks' to allow the developer to 'overwrite' your basic toolkit, and thusly offer the users the option to export and import resources to be distributable (freely or otherwise) to other developers, be this via a Shop accessible inside the engine, on your website, or, quite frankly, by the developers own means. If these Sim developers really want to create their own flight sim, racing sim, space sim or etc, let them compile it into their own games after purchasing a heft developers license from your company. If they so wished, they could make tool-kits for other users to make similar games if they so pleased, or the community themselves could develop their own mimicry of simulators to be implemented at the developers particular need for such.
With this in mind, I see an almost immediate flood of survival adventure games such as Arma2, DayZ, CS: World War, and so on, as well as a number of Minecraft spin-offs dealing with the destruction of earth to generate resources which can then be re-placed in 'glob' or even 'cube' deformations. Then there will be city creation toolkits to kingdom come, as well as custom world generators. The potential here is ridiculously unlimited, and yet uniformed around a realism attribute set by playing within a 'world' rather than a 'map'.
If your answer, however, is "No, you will be able to develop mods, but no on-hands compiler will be available" then I fail to see where you expect to go with this beyond your own game. You'll have lost a good chunk of your interested developers, and it may very well lead to your downfall (who really knows, right?).
Overall, I hope to see where you intend to take this before giving up all hope, so make me proud.
- almost forgot. As far as desert generators go, might I suggest using a perlin noise generator of sorts to generate 2 different maps, and 'shift' one into the next over time (based on wind)? Takes considerably less resources, and provides a semi-realism to desert terrain, as well as any soft-dirt.