As The Planner has pointed out Oxford - MK will be 45 mins.
Current Oxford - Manchester direct is 2h 44m
MK - Manchester is ~1 h 40m.
So unless you get a perfect 5-10min connection it'll be no better than the present and possibly worse.
Crikey, is this the glass always half-empty forum? Did you really mean to write "unless (it's better) it'll be no better and possibly worse"!?
A half-hourly service means that there is a 1 in 3 chance one of the two per hour is arriving between 15 and 5 mins before the hourly Manchester service (thus getting same or faster journey time and a minimum 5 min connection) - depending on the timetable in 2024 which hasn't been written yet. Yep, sounds like a possible option - but we don't know! Equally, it also likely leaves at a different time to the XC and so is an option depending on when you set foot on the platform.
Here's three more reasons why I think it's more likely than not to be showing often as an option in NRE..
1. Pre-covid - half the Manchester journeys would require a change at Brum - similar connections issue there, journey time obviously longer than no changes. (Now it's 1 XC per hour to Birmingham which utterly sucks, but I assume that gets fixed sooner than Oxf-MKC opens).
2. Even with pre-covid service - not everyone wants to leave at 7 or 39 minutes past the hour..
3. In the evenings, even pre-covid, Brum to Oxford quickly shrank to one per hour - 9:06pm then 10:06pm. Potential to get something mid-way between those times via MKC can't be ruled out.
Also - similar vein.. The late evening XC also sucks (and did pre-covid) for services from Yorkshire, arriving at Brum a few mins after the 9pm or 10pm southbound to Oxford. One of the options in NRE for 7.30pm dep from Sheffield to Oxford is actually routed via Leicester, Nuneaton, Leamington .. and it achieves same journey time as taking the XC and changing at Brum at 7pm.. Will be interesting if - post Bedford - Bletchley improvements - they recast MML to stop more services at Bedford.
For Scotland most of the services from MK are the via Birmingham ones - it'll be miles quicker to go Oxford to Birmingham direct than Oxford-MK-Birming
Mostly - right, I agree - but it always depends on when you travel and where you travel to.. the 17.41 ex-Milton Keynes to Glasgow (1x per day is direct over the Trent Valley) and takes 4h29.
The only direct BHM to Glasgow on WCML takes 4h02 at 19:15 (others take 4h20-4h40 with connections in Preston) - so 5h30-6h with connection time from Oxford - which is OK.. but if I'm leaving Oxford at 4.45pm and want to get to Glasgow .. that's around 5h30, when the other route is 6h at that time..!
So yeh, we don't know, but in 2024, it'll be an option - and I reckon it'll be suggested quite a few times on Nat Rail Enquiries!