I do not agree.
on 6.x it is expected by mIRC to use the 8bits pcre lib so the byte 233 would be sent.
on 7.x mIRC still use (until this change) the 8bits lib but use utf8 so the two bytes 195 169 are passed to pcre.
This is what scripters rely on, there is no assumption as to how characters will be seen by pcre.
Using the 16bits lib is not a bad idea as it allows no conversion, (and therefore no loss of lone surrogate?), do you think adding a property to $regsubex is a bad idea?
