Not sure if this was mentioned before, but I figured out a way to do this within the current constraints of Airtable. It does require an extra column in your sheet though, so it might not be for everyone.
The short version is, use a string for the column with your comma version of the value, and a formula field that is formatted as a currency with a decimal value, and add the following formula:
I have to say, if you haven't noticed - This feature actually came to Airtable short while ago without any major notification (or I might miss it...?)
Anyway! Now you can format your number fields to accept comma as decimal and also get rid of thousand separators if (when!) needed! It's not global setting though but a field specific. So this might bring some issues with international co-operation...
I took long and many frustrating feature requests and forum posts. I can finally let others (that might not be so into things you know...) use Airtable as well to input numbers!