On one hand, the entire route was at one time double tracked. When I was a kid, I think I walked most of it from avalon to mt airy.
On the other hand, it's never going to compete with I70 speeds.
Having hourly buses (half hour, for rush hour) running in the break down lane, with stations with walkways tunneled/ bridged over to lots for park and ride (and maybe level 4 AV trams or similar micromobility to nearby areas with population) at New Market, Mt Airy , Hunt Valley golf resort , Howard county fair grounds, and Frederick would get more use.
Maybe integrate it with one of the proposed MTA plans for dedicated BRT lanes in US40 from Baltimore to "Ellicott city " (Which is essentially the entire top 1/4 of Howard county) . It'll be a lot cheaper than rail.
Now, taking the engineering studies for the I270 monorail, and using that for MARC service to Frederick from DC would be worth the money. Especially if DMU or similar trains were used for more frequent service, at least to silver spring.
This would go well with the
https://s3.amazonaws.com/mta-website-st ... 202023.pdf
Brunswick line Master Plan.
Except building in 270 would cut at least 30 minutes off the trip, if not more, and would take a bit of traffic off that route.
Sadly, Camden line trains seem to be the best positioned for Virginia run throughs, for now.