I wouldn't be too confident about SAS rescheduling their MAN operations to facilitate connections for the benefit of afew passengers attracted by a single daily flight to IAH operated by a different airline. It is too easy on a forum such as this one to think within the mindset of 'friend of Manchester Airport'. Instead, we need to take a step back and think with the mindset of an SAS executive.
Exactly, and the same would apply to other *Alliance carriers like Swiss (ZRH), SN (BRU), LH Group (HAM/CGN/DUS) etc - I can't imagine any of them will be falling over themselves to fill a SIA service either when they have their own transatlantic capacity to fill first. Of course some of these flights and destinations will connect in one or both directions at MAN anyway, and passengers/corporate travel departments will be free to book these connections if they wish. Geographically this is one occasion where being located on the western fringe of Europe is an advantage to MAN in terms of potential feed to/from the rest of Europe.
As for UA it will be interesting to see what they do. On the one hand a codeshare MAN-IAH would open a new spoke into their largest hub and with all the commercial risk borne by SIA. On the other hand they already choose not to codeshare on SIA's FRA-JFK A380 service (but do on the LH FRA-JFK service) so maybe there is a clue there.
Interestingly the IATA slot allocation conference for the Winter took place on 21-23 June, and on 24 June the UK voted for Brexit. Do we know when SIA requested the slots ? Anyway a lot has changed since 24 June and there's a lot more uncertain economic times to come, so like Mr A Tis I will feel more confident about this route when it is formally announced or put on sale.