Unfortunately, at the time Pier 1 was constructed, MAG's plans never envisaged the covid catastrophe which has placed all further T2 rebuild work in the freezer till further notice. Piers 1 and 3 were both part of the medium-term vision, with each playing a slightly different role. Now, the airport must make the best of what it ended up with when the music stopped. With a 'glass half full' perspective, MAN is darned lucky that the main Terminal 2 extension and Pier 1 were completed just in time (though MAG's accountants might disagree). I don't know when / if construction of Pier 3 will progress (any input on this welcome), but it is wise to be braced for a very long wait. MAG isn't noted for spending freely at the best of times.
On the matter of the Qatar A388 schedule, it remains to be seen whether this happens or for what duration if it does. The airline is in dispute with Airbus over alleged rapidly deteriorating paintwork on a number of A350's which have been grounded in consequence. Until this is resolved, it means allocating other types to cover some routes (note that not all of the A350 fleet is affected). Once the A350 fleet is fully returned to service, cover from the A388 to MAN may not be required. Keep in mind that Qatar Airways has a large fleet of B77W's as well as A350's available, and DOH-MAN is a 3 x Daily route (covid aside). The additional capacity implied by running one of those flights as an A388 isn't a huge step-up.