Completing myself,

> OTOH, while we're at it, I wonder if we should keep grouping with
> parenthesis. I guess that if you want to use parenthesis, you're going
> to need math mode anyway, so there's no real need to make it easy to
> type, e.g. :
>
>   x^(2-i)
>
> which will become x$^\text{(2-i)}$ anyway.

I attach the suggested patch. I removed parenthesis-grouping for the
reasons I gave above. Carsten: if you'd rather keep this feature, let me
know, I'll provide another patch.

I also slightly changed the simplified regexp, as [:word:] includes
underscores in Org syntax. I used [:alnum:] instead.

Regards,