Once we're there my educated guess would be that such a fork could be deployed fairly undisputed, as I don't see any reasons for contentious camps about decimal precision arising, making it easier and thus faster to deploy. Then again crypto is a weird place, so who knows what counter arguments against an increase of decimal precision arise. It would be interesting to see how much the effective impact on block size would be, for example.
From memory there was a very specific data related reason why bitcoin was capped at 21 million.
Something along the lines of (bad example:) there's 8 bits in a byte, and therefore we have 0 digit figures - increasing the digits requires adding a full extra byte which increases data requirements / processing requirements / bandwidth / etc.
Pretty sure there may be a legit opposition to this, but then again, it may be inconsequential at this point in time. Perhaps it only mattered 8 years ago.