Absolutely nothing.

For reference, here’s footage of a 5 Megaton nuclear device being detonated underground. No global eruptions, and hard for humans to even feel further from the epicenter - although, seismic monitoring by precision instruments is a known way of monitoring for secret underground nuclear tests.

For further reference, the 2011 Tohoku earthquake off the coast of Japan - the one that unleashed powerful tsunamis - released a staggering 3.9x10^22 Joules, or around 9.3 million megatons of TNT. While this did cause local devastation, it also failed to meet Project Vulcan’s goal.

You’re basically asking about “Hard” and “Soft” science fiction.

For me, at least, I lean a little bit more towards the “Soft” (what you call ‘Fi’) side of things. But I’ve also always found this a little bit of a false dichotomy; a story can go fully fantastic and explain nothing about its spaceflight, but lean heavily on actual psychology or other social sciences to drive its characters; so is it “Hard” or “Soft” sci-fi? Turns out it doesn’t matter; it’s Sci-fi and if it’s a good story, then it’s good.

I also have to somewhat push back on the idea that Star Wars “doesn’t even try to explain” its tech. A lot of people put a good bit of effort into laying out how the technology worked, up to and including calculating the energy involved in things like Turbolaser bolts (turns out, it’s a metric shitton of energy).

I’m pretty sure I’ve seen small (i.e., handheld-sized) commercial UAVs that fly like this. But as others have pointed out, at any realistic size you start to run into a lot of problems:

• The VTOL rotors will create massive drag when they’re not in use. There’s a reason virtually every aircraft with embedded VTOL jets engineered ways to cover them up during level flight. This cascades into a whole bevy of complexity issues.
• When you’re not using them, you’re lugging around 3 out of your 4 rotors for no reason.
• You’re also sacrificing a lot of internal volume for your lift fans. This isn’t so much a problem in small UAVs, again, but it’s not great if you were hoping to use that capacity for fuel or cargo.

So yeah, like others said as well - now that we have tailsitter drones of moderate size, there’s not really a use for this layout.

On the one hand, to me, “mobile suits” should feel titanic and weighty, larger than life. So yet another Gundam zipping around like a demented chimpanzee on crack is… I dunno. Fighting space robot aliens is also a choice, since the man-vs-man and political background is a key part of what distinguishes Gundam.

On the other hand, a Gundam game in 2027, by Bandai-Namco, scored by Mick Gordon? That is such incredible levels of hype and I really, really hope that this is good.