The one factual thing is that the latest DfT procurement pipeline spreadsheet (reissued yesterday 10th May), now has 2 Chiltern tenders (new or used), but both seem to be for multiple unit stock (to replace those currently leased from Angel trains), either BEMUs or low emissions multiple units, clearly either or (not both) as both for same 30-70 units
There simply isn't any mention of long distance stock for Birmingham services on the spreadsheet. So either the mk3s (some of which are over 45 years old) are being replaced by DMUs or DfT already has a plan for something else.
Realistically the only longer distance rolling stock can only be mk5s or 175s or spare 221s or 222s. (and none of 175, 221 or 222 could be described as low emissions, which is required, so can rule them out)
Listing of upcoming Department for Transport (DfT) and associated bodies commercial contracts – known as the commercial pipeline – for which bidders may apply.
www.gov.uk