Can bases be made to move on the Geoscape screen?

[Stoddard]

No, but what if I want to add super fast fighters or bases, because it makes sense in my setting? If the game engine put a soft limit on it, because at some level it's falling apart, then it's just poor design. X-Com design standards are higher than that.

Hmm. As long as player takes care to not abandon his craft, the craft won't crash. As long as the player is informed that his action will result in a loss of a craft (see the last paragraph), I don't think there is anything more to do here.

I can't think of a setup (craft, base speeds, fuel tank sizes, number of craft, their missions) which will result in a crash unless the player willfully ignores warnings.
I feel that the assumption that there is always such a course change for a base to recover all launched craft can be proven to be strictly true, as a math theorem.

Of course, the fuel reserve will have to be recalculated every game tick.

Now, if we start to tie fuel consumption and/or max speed to battle damage, then, of course, dry crashes are possible, even with stationary bases.

I think I'm somehow not getting what you mean with 'soft limit' and 'falling apart'.

But yeah, making the plane crash is good enough for me... as long as it's communicated to the player clearly.

There's already a 'low on fuel' popup. There can be another if the base moves out of range, mentioning the base in question. If it runs out of fuel after that, it crashes, another popup.

The whole situation is only possible if player changed the base's course in such a way that it increased its speed away from the craft, while a craft is returning in 'low on fuel' condition. At this point it's either reverse the course change or lose the craft.

[Solarius Scorch]

OK, that sounds good!

[Ewokgod]

It's a fun idea, but what problem would it solve for you? Would they be immune from crackdowns?  I have wanted to put a base in the ocean for better radar coverage in a few specific situations, but never thought about it moving

Mobile bases (MBs) do not fix any problems as such. If the player wants to have better detection coverage, Spy Zeppelins and Expeditions allow the player to tailor the coverage he wants, for a resource fee and a hangar slot each.

What MBs can do is provide close-in attack options. For example, have you ever discovered an enemy base outside your detection range that you really did not want to attack yet? Maybe you didn't have the right equipment (read bigger guns) or your good gals were in the infirmary. Maybe it is going to be wall-to-wall Cryssalids (or worse) in there. That base affects your score negatively until you destroy it and there is nothing you can get out of it. A MB could put a radar footprint over that enemy base and, at least, you can detect and shoot down / attack the supply ships as they come in because you not only have radar coverage, you have a hangar. nearby Once you finish with the enemy, your MB can be retasked to other areas.

Another thing a MB can do is allow the player to layer his base defences. if a crackdown is coming for one of your bases and a MB is nearby, that's another hangar for defensive fighters and another radar footprint that may allow the player to detect the attackers earlier. Heck, I don't know exactly how the AI chooses targets for crackdowns, but there might even be an option for a sacrificial MB, empty of anything valuable or crew, just sitting on the AI's flightpath to be detected and destroyed at the AI's whim. Or a trap MB, loaded with trap rooms and your best killers.

If the game develops any base buildings that have (or can have) a negative effect, it might be useful to hive off those buildings into a MB. For example, I've never seen it happen but the in-game bootypedia says that a summoning circle may spawn enemies in a base defence. The player could put a summoning circle (and any other buildings like that) on a MB and park it far away from the other valuable stuff. Extra cool points for putting your circle over a rough guess of the location of R'lyeh before you start trying to summon Cthulhu

As to being immune from crackdowns, I don't think so. There is some functionality in them not being immune, and there can be some cool scenarios in their base defence battles; circled wagons for a convoy, room-to-room fighting on a sea-going vessel (maybe even seabed stuff, submersible carriers are possible). An airborne carrier, on the other hand, might just be shot down by the enemy, if the intercept screen can be rejigged.

And dammit, they are just cool and not that far removed from real-life weirdness. If you would like some evidence,

https://en.wikipedia.org/wiki/Zveno_project

https://en.wikipedia.org/wiki/I-400-class_submarine

https://en.wikipedia.org/wiki/French_submarine_Surcouf

[Ewokgod]

An aside on the question of fuel range on aircraft.

Does anyone know if the RTB fuel warning can be overridden, in effect, it never shows up, for a specific fighter?
And can a modder make a fighter lose all its HP after an intercept?

If the answer to both is "Yes", or maybe "Yes, but why in the name of all that is unholy would you want that to happen?!", then, if you give that fighter a very high speed, decent dodge, good accuracy and a damaging one-shot point-blank weapon, you've made a surface to air missile, and there might be a use for that.

[Dioxine]

The answer to both is "no".
If we want SAMs, I think a better idea would be working with base defense buildings (extending range if needed), not interceptors.