Only 64 miles from Bromsgrove to Yate, so surely should be easy to do.
Snow Hill lines;
Stourbridge - Dorridge = 23miles
Tyseley - Stratford = 21miles
Total of 46miles to get nearly all the WMR services electrified.
(+ 14miles to include Dorridge - Stratford, which gets you to 60miles)
I suspect for Birmingham - Bristol to get done, it needs to become an infill project, where much of the work has been done under previous projects;
Bromsgrove & Stourbridge to Worcester
Swindon - Gloucester
Bristol - Gloucester