It’s not the following verbnoun that decisive, it’s the preceding verbnoun or adjective.
bodlon willing doesn’t use i (mostly this is indeed the case with this type of adjective in Welsh), so:
Faset ti’n fodlon aros amdano fo?
While in the first sentence there, the i is associated not with bodlon, but with rhywbeth, isn’t it?
Faset ti’n fodlon dod â rhywbeth i yfed…
The bodlon still doesn’t take i - we say …bodlon aros…, don’t we?
Similarly, for example, with a verbnoun:
Wyt ti’n bwriadu dod?
Are you intending to come?
Wyt ti’n bwriadu dod â rhywbeth i yfed?
Are you intending to bring something to drink?