At this point I'd like to point out that according to what we know, there is currently a majority of something like 450-150 in favour of triggering A50, so this ruling does not mean that Brexit will not happen. The Liberal Democrats have said that their six MPs will vote against A50 unless promised a referendum on the final deal. Labour has hardened its position in favour of Brexit in recent weeks, and has said it will not "frustrate" the process. What Labour are trying to do, is get some amendments into the bill to make sure that we get tariff-free access to the Single Market, among other things. At this point though, there is no real threat of the vote holding things up.
The Supreme Court also voted unanimously that the devolved Parliaments do not have to be consulted, and so essentially cannot veto the 50 vote. This will be difficult news for many, but also ensures that we will not face a constitutional crisis during the A50 vote, something which certainly might have held the process up.
This case had to happen because of the vagueness of Article 50 itself, and the fact that the referendum bill is for consultative rather than legally binding referenda - something which could be blamed on the Cameron government. It is unlikely though to impact the timeline or the nature of the Brexit process. The other two pending Brexit legal cases though, on the revocability of A50 and whether we automatically exit the EEA at the same time as the EU, have the potential for more impact.
more thoughts on tm's speech
Let's not beat around the bush here, every piece of evidence we have suggests that this is impossible. Around a tenth of Canada's exports go to the EU (compared to around half of ours) and the CETA agreement - which does not cover services (around a third of our exports) - took seven years to negotiate. The much more comprehensive South Korea FTA arguably took 18 years since inception, with the final round taking four years. Switzerland - whose relationship with the EU most closely resembles what May seems to be going for - has been negotiating constantly with the EU for 10 years now.
If the Government really does expect to wrap up a comprehensive FTA - the biggest and most complicated single aspect of this process - in just two years, then it isn't clear what the "phased implementation" and "interim arrangements" are for. The EEA/EFTA route which I personally favour would see us do the official exit from the EU in two years, not bothering with trade at all, and then figure the rest of it out once there are no time constraints. It feels like Theresa May's route means that we can't exit until we have an FTA, which could be ten years, or that we have to leave with no deal at all. That is of course, unless those interim arrangements end up being something along the lines of EEA/EFTA and we're just taking David Davis' words too seriously.
Now would be the ideal time for the Brexit opposition to call TM out on this and push for an interim solution that keeps us in the single market for the time being, so as to remove trade matters from the A50 negotiations. The danger with this strategy of course, is that some will see such a solution - being officially out, but sort of still in - as a way we can sneak back in to the EU at a later stage. This has to be avoided, or both sides once again find themselves at an impasse, and the chances of us ending up with a solution that suits nobody increases.