To be honest, there's still a part of me that wonders whether Ayton would be a better location for the station; greater immediate population, closer to Eyemouth, slightly more ideal for Chirnside, can serve Burnmouth - but there's merit to the Reston location too, as it's probably more balanced for Berwickshire as a whole - closer to Coldingham, St Abbs, and Duns. But I'd agree with Bald Rick in terms of the importance of new housing development in and around Reston.
It's worth noting that, statistically, Cockburnspath has the longest commuter journey times in the UK. Just throwing that in there.
There's certainly a valid debate to be had about the utility of a station like Reston. An East Linton station serves an immediate, growing settlement with scope for commuter travel into Edinburgh; Reston is more removed from that. It's been conceived, ostensibly, as a railhead for the wider Berwickshire region (which probably does have untapped demand for rail; the question is whether a Reston station is the best way of meeting that demand).
But then the debate this comes down to is essentially ideological. Like nearly every single thread on this forum - every thread about a reopening, whether speculative, embryonic, or realised - your personal response will depend on whether you think the British railways serve a social function regardless of the market itself.
I realise that that's a grandiose statement in itself, and that I'm probably not articulating it quite as well as I could, but screw it. I think that this is ultimately what a lot of the debates on RailUK boil down to, whether we're retreading Beeching for the umpteenth time or discussing a new project. It's a generalisation, but ultimately, I think there's a lot of the "idealism vs pragmatism" divide in these discussions; it's baked into peoples' points of view.
(And then you get the inevitable strawmanning of either side; the "crayonistas" who "want to reopen branch lines to piddling little rural towns" like Hornsea and Kington and Crythin Gifford; conversely, there's the "Beeching acolytes" who "are anti-rail" and should just go and find a car forum or something. The tone of this discourse flattens the debate, mischaracterising and compartmentalising either side of it - with little room for nuance. It's what makes these kinds of threads often so markedly oppositional; that kind of attitude of "urrghh, it's the usual suspects at it again". And I'm guilty of it too.)
Ultimately, there's no easy answer here, because it's a perpetual issue on RailUK. So here are my thoughts on Reston itself.
I think there's something to be said for footfall as a key indicator of a station's success. I would argue that recent Scottish reopenings tend to do well in terms of footfall; the precedent here is the Borders - which exceeded expectations - but then again, Caldercruix/Blackridge/Armadale perhaps haven't so much. Overall, however, I think there's a case for saying that Scottish customers maybe have a higher propensity to take the train than customers do in certain parts of England.
As it is, with Reston being on the ECML, I think the footfall will be strong, relative to the station itself. The destinations in either direction are Berwick and Dunbar/Edinburgh (if XC or TPE serve the station, then potentially an array of major cities in England and Scotland will be connected, though only Newcastle is a significant destination locally); it's also on the A1 corridor. The railway is ideally suited to pick up on the main flows, save for the ones between the towns and villages themselves. I'd argue that the location of the station on the ECML is likely to promote use itself. It's a bit different for, example, being on a line like the Colne branch. There's quote-unquote 'destination' stations in either direction; Reston-Dunbar/Edinburgh flows, Reston-Berwick flows.
The debate, then, is about the strength of those flows. Even if footfall is high, the population needs to be high enough to justify that footfall.
I think that the 253 bus is a relatively poor indicator of regional flow demand strength because, well, it's a fairly rickety bus service that takes a good year or so to get to Edinburgh. It's not a premium service, either. And, if you have to get the bus somewhere, then you might as well just drive, and save yourself the bus fare (even if you'll expend that fare on fuel for your car). Not everyone wants to sit on an Optare MetroCity for the two hours it takes to reach Edinburgh city centre. If you live in the area then you're bound to own a car anyway; sadly, car flows aren't something we can really record. (I sometimes wonder about how different these discussions might be if we could record them.)
There's also a small leisure market to factor in. I think there's people who'd get the train out from Edinburgh to Reston so that they could visit St Abbs, though it's obviously not a particularly huge number. Unlike the Borders, there's a disconnect between the station and its population (yes, Tweedbank is a fair distance from Melrose, but Galashiels is well-placed for Galashiels; also there's no Midlothian stations...but then there's no need to rebuild a railway line through them). There's going to be a very high proportion of car owners in the area; how many of those cars will end up parked at Reston?
To be completely honest, I don't know if I can back up my claims about Reston. Until the station doors open, we are talking theoreticals, all of us. I just have this impenetrably strong gut feeling about it; that it'll succeed. (You could argue that that's because I want it to succeed, but rarely do things ever succeed when I want them to: case in point, Edinburgh Rugby in the Pro14). I trust my gut, (even though it's deteriorating rapidly what with all this pandemic anxiety and everything. Only four more days of 2020 to go).
Anyway, maybe Holyrood won't even agree to the business case. We shall see.