Nothing against your suggestions, but I see no logic in adding support for blockchains and their tokens on stellar or TON if they replied negatively to adding USDT over Tron, which is the 1st or 2nd most popular blockchain for the tether stablecoin. Unless those two networks are starting to dominate compared to the TRC20 version of USDT in terms of trading volume, why provide support for something from the bottom of the popularity list?!
As far as I have interpretated exch's posts on the subject, they evaluate each blockchain separately, popularity not being the main aspect. They have for example stated that they distrust some of the founder teams, even of very popular altcoin blockchains.
What I had done is to revise Tether's and Circle's websites for potential new blockchains they're supporting, and TON and Stellar were the networks I have not read about in the discussion about the topic. Stellar, at least to me, seems relatively trustworthy due to its long history, while in the case of TON the recent popularity could be an argument for them. Tron was controversial from the start, as is Solana (albeit for different reasons), and I can understand their decision to not add them.
I'm personally quite neutral about that topic because the only chain from the so called "Ethereum killers" or "smartchains" I use is Avalanche, but it would be totally ok if they distrust AVAX and indeed add Stellar for example. There are open source clients for almost all blockchains so the barrier to use one or another stablecoins should be low.
There is another thread with details on Lightning Labs (the team that created the Lightning Network on Bitcoin) running successful tests for
Stablecoins on Bitcoin blockchain.
Yep, I've seen the thread (and also posted there some months ago), but until now I have not heard news about a "real" stablecoin project on Taproot Assets. Even a recent
Bitcoin Magazine article called "Stablecoins are coming to Bitcoin's Lightning Network" still has no real information about that issue. So we may have to wait a bit more.