I think the stations to from Sheffield to Dore are non-starter unfortunately. I've no doubt the demand is there if they are served my multiple trains per hour, but I don't see where those train services are coming from.
There's only one service local stopping service operating south/west of Sheffield. One train per hour isn't going to be frequent enough to make the train attractive. It works more at Dore because the bus takes longer into Sheffield than it would at other interemediate stations, but Dore is mainly used by people travelling to Manchester.
Perhaps if some sort of turn back loop is created at somewhere like Gridndleford and the line between Sheffield and Dore gets more tracks, it might be possible to run some local services from east of Sheffield as through services providing a decent frequency to new station along the route.
Nunnery Square platforms are a decent idea and the Barrow Hill line should be opened to passengers either using tram-trains or heavy rail.
Heeley, Millhouses, Beauchief and Dore & Totley 4 platform stations were able to support stopping services into Sheffield and beyond. That was in the days when most of the population didn't have access to cars, lived fairly close to the railway and it was quite normal to walk maybe up to a mile to catch a train. In 1939 the future still looked rosy for rail and the Sheffield Star published this.
At which point things went badly wrong with a bang, rather a lot of bangs!
By the mid 1950s we'd discovered private motoring and the desire to have a semi or detached house on a green estate away from railways and then away from bus routes too. We also lost the use of legs to use cycles to go to school or work.
Down the Sheaf valley there had been 4 tracks but by 1970 all the platforms were out of use except the 2 at Dore for the Hope Valley line. Behind the backs of all but a few 2 of those 4 tracks were removed along with the redundant platforms, the remaining 2 tracks slewed to achieve better speed and junctions and sidings were removed. Bridges across roads and the Sheaf were removed. Parts of the retained old track bed now carry a selection of railway structures and access points.
Consequently a recent Sheffield MPs bid to open all these stations was rejected by the Reopening Railways scheme before the first fence. To make it work you'd need to recreate the separate fast and slow lines from Dore into Sheffield. HS2 called for a 3rd track from Dore into Sheffield and that complemented the Heeley loops. There isn't room for 4 between the two Archer Road over bridges.
HS2 into Sheffield is dead but initial planning for electrification seems to follow that tracking model - but no new stations. if there were Millhouses would work best - but it's at the most restricted section. A feasibility study was completed - just after Tesco's had built a new store restricting the potential site. With hindsight perhaps it could have been built on stilts above the railway - maybe that's a rebuild project for the future.
Restoring all 4 platforms at Dore was the subject of a feasibility study about 2015 and the new platform has passive provision for it. Too late, the current project was already too advanced to change- and the lack of 4 tracks into Sheffield would probably scupper it anyway.
3 trains an hour pass through the new 6 car platforms at Dore every hour but stops on the fasts are timed for Manchester bound commuters. By far the easiest and cheapest way to provide 2 (or even 3) trains an hour into Sheffield would be to stop the EMR service that runs about 25-35 minutes apart from the Northern service. Previously they were prone to conflicting around the single track Dore area but now can pass each other through the station. But an additional stop adds 3 minutes into the timetable. Huw Merriman suggested a reduced journey time between Sheffield and Manchester - down from 50 to 30 minutes! Just another impractical and conflicting railway aspiration.
Yes, a turnback loop at Grindleford might have merit. Any train entering Sheffield from the north or east could run through to terminate there to relieve Sheffield terminal capacity.
Back again in the 1930s special trains would run through to Hope Valley stations (and Dore) and be held in station sidings to return in the evening. Only Grindleford retains even an engineers siding, but still has plenty of level space to add back more.
