I can see why they thought of the idea originally - if anything it would be great for Birmingham as many big London firms open up branch offices or move altogether.
But in the current climate with the Covid bill needing to be settled at some point, I think the government should cut its losses and scrap it. I would imagine HS2 was justified with pre-pandemic figures of rail use; a lot of big firms are not renewing office leases and are permanently working from home thus negating any need for good transportation links. We'll have to wait to see how many big employers follow.
Also a £100bn train line from London to Birmingham, with costs likely to soar even higher while I imagine Phase 2 will be dropped at some stage, is not what the UK necessarily needs. I haven't heard from any major groups or companies who passionately support the project yet we've all heard the intense and vocal opposition to it. That probably says a lot.