They already have on the 551. Liverpool, Chester, Nantwich, Stoke, Birmingham, Birmingham Airport, Heathrow, Earls Court then London Victoria. Who is trusting a once per day bus for their airport transfer? I certainly wouldn't be. It's also followed 15 minutes later by the 210, so it makes absolutely no sense adding 30-35 minutes onto a longer distance service, to satisfy demand that is barely there (north west - Heathrow) or satisfy shorter distance demand (such as the Birmingham to Heathrow traffic).
They also threw in Warrington Winwick Road onto the 170 (top end near Aldi) but that has now been removed thankfully as it was a very silly stop.