Before you read the detail .... the current system with irregular trains stopping at Didcot and connections from Swindon (and beyond) to Oxford (and beyond) being hit and miss, causing delays of up to an hour for travellers on what are otherwise half hourly services where some miss the Didcot stop, looks like it could have been designed to discourage traffic from the West. I say "looks like" because I suspect other motives for the odd service pattern.

But the question has been asked "for a future direct service such as the one that was lost a couple of years ago, should a Didcot stop be included?"

First comment.  When I travelled up to Oxford last week from Melksham, nearly everyone who got off at Didcot from the London train walked across the platform to join a near-empty service coming up from Reading.  So the main flow into Oxford on that train was passengers from the west


The train to Oxford arrives at Didcot

Second comment. It would add (I estimate) 10 to 12 minutes into the schedule of the West to Oxford (later to become Bristol / Portsmouth to Cambidge  ) train to stop at Didcot.  For that extra time taken, extra opportunities provided would include a more reasonable service from the West to Didcot itself, and further connections to / from Oxford and the West from Thames Valles stations between Didcot, Reading and London.

Third comment. 10 to 12 minutes is very similar in time to the time taken to change (in a very good case) at the moment, and it's 5 times better than the worst-case scenario of the oft-missed conenctions


Passengers await the train to Oxford arrives at Didcot

Fourth comment.  A through train (provided that a TOC doesn't keep cancelling it - I noticed 16% of services cancelled Swindon to Westbury in the last week - another FGW Cinderalla route) doesn't suffer the "double jeopardy" of a connection where cancellations / delays on either service delay both parts of the joureny

Didcot however will add a ridiculous amount of time, for destinations that allready have services to/from Didcot, so I am against calling it here

The Jacobs Consultancy Strategic Rail Authority Greater Western Franchise Replacement Outline Business Case Report (link below) recommended the introduction of a Bristol - Oxford service that called at Didcot , saying that there was a "significantly positive economic case" (Pages 38 - 41)
http://www.dft.gov.uk/foi/responses/2006/september06/swindonwestburytrainsservice/greaterwesternoutlinebusines1103

This was dependent on no additional rolling stock resources being required. Two points of note :

1) The business case would be even stronger if trains ran through to Cambridge / Milton Keynes.

2) If the East West Rail link proposal were to be approved , the package would include new rolling stock.

It was removed at the insistance of the then-SRA.  The stated reason was that it was to increase the reliability of the remaining services.  It was fairly lightly used, but that might have been because it was frequently cancelled and was not therefore a service that could be relived on.

As an occasional peaktime traveller between Bath and London, I would perversely like all the HSTs to stop at Didcot, because it would allow me to save over 50 quid in fares by rebooking at Didcot. 

how about increasing the stops at Didcot and missing out Chippenham

A good overview of Didcot (which has 5 platforms in use) can be found in the link below.
http://en.wikipedia.org/wiki/Didcot_Parkway_railway_station