What base HP value does ditto become a top (but not banned) threat?

Ditto is a very interesting case when it comes to balance because as far as stats go, there's literally only one balance lever that can be pulled for it which makes it pretty easy to theorymon changes to it.

My question is, what HP do we think ditto would need to become actually viable in singles metagames?

As it stands right now with 48 base hp ditto pretty consistently hovers around C viability in OU metas. Respectable but room to improve. Meanwhile on the other side of spectrum imposter chansey with 250 base hp and access to eviolite is an S-tier threat in the most unhinged mechanically pure meta of balanced hackmons.

Somewhere in that spectrum is S-tier OU viability. What HP do we think that would be?