Under the new arrangements, Virgin will be supplying a very high number of transfer pax to Delta over ATL and vice-versa. Niggling problems with the scanners not processing the codeshare carrier's boarding cards are unlikely to persist for long in this environment. Getting the software engineers in is far cheaper than dealing with the fallout from missed / stressed connections. Hopefully, the gate staff will be reporting back on such occurrences too … with DL/VS working ever more closely together the two companies have every incentive to iron out IT issues of this nature quickly.
BTW, my impression is that Virgin Atlantic enjoys very positive market recognition in the North of England catchment. Whilst I have no firm data to fall back on, I suggest that the carrier is far better known / recognised than Delta in these parts. I would also see any interline demand for Florida via ATL as a bonus … remember that charter capacity on MAN-MCO/SFB is way down from its heyday (APD hasn't helped). The loads which formerly used the daily Travelcitydirect B743 are now combined with the pre-existing VIR B744 schedule; American Trans Air are long gone; Monarch appear set to abandon their last foothold in long-haul. Just Virgin, Thomas Cook and Thomson left. The last time I got a quote for MAN-MCO on Virgin the fare was eyewatering … if additional capacity via ATL can help that's fine by me!