Gundam game would need a similar rule-set, and for CGL to massively shit the bed
They already are.
Who cares about Battletech these days? Grognards who grew up on Mechwarrior 2 and have nostalgia for the tabletop. CGL has been pissing off that audience with their woke pandering. That leaves new people who are intimidated by the complex rules, long play times, and complex looking character sheets. CGL can't change the rules because Alpha Strike didn't stick. They are coasting by on memories of the good old days, but as Star Wars showed that isn't an infinite money pit.
I had an experience recently where a long time 40k fan (let's call him Joe Hobby. He's like a normie, but he just does hobby stuff, and pays no attention to online discourse). He sold his space marine collection and moved to Bolt Action, though the historical World War 2 setting is a bit dry. He showed interest in Fallout but was turned away by the price. He thought about Battletech but was put off by the character sheet. He put some thought into Star Wars Legion. I was even tempted to split a starter box with Republic vs Droids (he likes ep 1 droids and I like Republic Commando and that one animated film from 2003).
I say this because Gundam could, in theory, turn that Joe Hobby, who doesn't know what a Gundam is beyond my mild interest in Japanese model kits, into a Gundam player just by offering cool looking models at a good price. ie. The thing Bandai does with their Gunpla.
CGL and BT can't compete. What do they offer than Gundam won't? Nostalgia for Timber Wolf and some 90s PC games?
As for a threat to GW. I don't think Trench Crusade, Gundam, or others mentioned so far are a concern. What might be is Konflikt 47 3rd edtion. It won't kill GW or anything, but it's looking to do what people like me want. Warlord makes good sculpts at affordable prices compared to GW, while not being as dry as Bolt Action. The only thing it lacks is the ability to make "your guys", though they could do that with some lore changes. At some point they announced Andy Chambers contributing to the game design, and some other classic era GW guy on lore.
Again, going back to Joe Hobby. He wants a fun wargame with cool minis at an affordable price. He already has a Bolt Action army, so his buy in is relitively small. Warlords £110 start armies have a good reputation, and ample cheaper third party options exist if he wants to another army. He could easily get away with some Victrix WW2 for rank and file infantry to save money for his set peice weird war 2 units.
I saw some clickbait headlines last year about how GW had pissed off FLGS (I never watched the videos). At the hobby shop Joe Hobby likes, Warlord pastic uses about half the shelf space of GW, but that's still a lot of space proportionally speaking.