Default rules in bitcoin core with segwit enabled bias towards segwit transactions by counting the amount of block space they use and since their signature verification is no longer in the block they are substantially smaller than traditional transactions (up to 4x) so if they use the default bitcoin core implementation they will bias towards segwit transactions by default. However there is absolutely nothing that says what any pool must include or how they must bias their transaction choices, so long as the transactions are valid by current rules - most pools run custom bitcoin daemons already and they probably have their own custom rules.