I'm French, and France has one of the biggest high-speed train network, and the limitation to build additionnal lines isn't a technological one…

I'd agree that it's not technological: it's cost and practicality.

trains that float above the rail means less maintenance. the high cost of trains is partly due to the maintenance of the rail network.

The speed of trains is generally not limited by engineering. It’s limited by corners, i.e. obstacles. There are already very fast trains in existence that don’t use maglev.

You're assuming they'd replace existing routes rather than build new routes that would suit the higher speeds.

That's the main problem, building a rail line zigzagging around the country is arguably a ton easier than having to legislate, seize, steal and forcibly bulldoze a straight path for a maglev.

…and sometimes there are obstacles that you can’t bulldoze. Mountains, rivers, towns, etc. You can build tunnels and bridges but it’s very expensive just to get people to their destination a little faster. The temptation to add a little bend is strong, but the smaller the minimum turning radius, the slower the maximum speed, and the higher the chance that you don’t need maglev at all.

It’s very dependent on geography. Ironically the US is a much better candidate for maglev than Europe with its wide unpopulated expanses.

Ah, but how many countries would develop superconducting maglevs just to fund their defense program that's using similar research to make superconducting rail guns?

Probably zero. The problem with current railguns is not that they have too much electrical resistance but that their barrel wear is much too high for practical use. Superconductors wouldn't solve that.

In any case countries that want to spend money on military research just do so, using the budget they allot to military R&D. There's no need to try and hide that you are researching railguns.