Many thanks for mentioning this - I probably missed this version being in the local news, but do remember the Bellgrove option mentioned locally in a big fanfare within the last five years.
I do feel it would be crazy for the Scottish Government/Transport Scotland/etc to dismiss the Bellgrove option, as mentioned in a later post, it would just transfer passengers at the end points from one route to another, with little scope for connectivity on a local suburban level citywide.
I do recall a document from one of the Scottish transport campaigning organisations said Network Rail would prefer for the Glasgow terminus to be at Central. If you look at how the other HS2 termini have come about, you'll see a recurring pattern where regeneration is a factor but isn't as important as the need to connect into existing transport hubs. That's why even Salford Council supported the Manchester terminus being at Piccadilly rather than in their own territory, despite the location being served by Northern Hub trains.
Similarly, the idea of Newbridge being the main station for HS2 in Edinburgh is a non-starter. Waverley is pretty much the best situated central station in the UK and the cost saving from avoiding it would be dwarfed by the resulting losses in ticket revenue and other connectivity. If HSR ever goes north of the Forth then Newbridge/Edinburgh Gateway isn't half bad as an 'Edinburgh Parkway' station given that HS2 will approach Edinburgh from the west.
Regarding tunnelling: there may be a potential big problem for a north - south alignment. it needs to go underneath the mighty Clyde!
Cheers
Adam
Tunnelling under the Clyde would be trivial for a modern construction team with TBMs. A north-south city tunnel would only be on the same order of size as the M74 completion or the Queensferry Crossing, and with all the HS2 and London tunnelling projects the facilities do exist for tunnelling workers to be trained or redeployed to Glasgow.
The reason the tunnel hasn't been built yet is because it is entirely dependent upon EGIP, and combining the two of them into one (like how Crossrail is paying for electrification to Maidenhead) would make the project more difficult for no real overall gain. Once the new trains are in service at their maximum length, they will fill up and something new will need to be done. Around the same time, the lines to Barrhead and East Kilbride will be electrified, so that's another set of services that could be sent into the future tunnel and likely extra services needing accommodated at Central. Combine these together and the only realistic answer is the tunnel.