Maybe not multi-gigabyte, but in a new system/phone in a year, you're basically guaranteed to find at least one tiny model. We may even get some "standard" model everyone can reliably use as a reference.
At that point it would be useful. Although, I wonder if it wouldn’t make more sense to train one specifically for the job. Current LLMs can predict HTML, sure, but they’re large and slow for the task.
Yeah sometimes compression ratio is not the right question when there are other practical concerns like disk space or user experience.
But I do want to point out that almost everyone installs at least one multigigabyte file to decompress other files, and that is the OS.
If the only thing the OS could do is decompress files, then we'd be rightly upset at that for being multi-gigabyte as well. :)