@Alongcameacat - Yes a lot of WFH jobs will be outsourced. I see a lot of outsourcing contracts in my role. Sadly we are all replaceable and your replacement just may not be as great as you, but most companies are looking at costs, not giving you job security.
What will likely happen? Salaries will level off. Maybe even more centralised currencies being used.
What do you need to do now? You need to find out (a) what you are good at and (b) what your accessible economies want. Like @JessicaBlack101 said "So anyone who is concerned - figure out the specialty or niche in your type of work and learn it now." And remember what @Dastardlythefriendlymutt said "I do think we overestimate British exceptionalism sometimes."
In terms of the point @SirSamuelVimesBlackboardMonito re: accountant salaries in Newcastle vs London, I think that it would be brill if anyone around the country could apply to any role. But within our own country, we will find that London/high salary city centre salaries will be the first to go.
In terms of both @Tadpolesandfroglets (IT) and @Worstyear2020 (training up their replacements, sorry to hear this!), this is the way of the future. Companies typically have you train your replacement. IT will also be the first to go. One of the big four accountancy firms use Scotland a lot. One of the banks use East Asia (sorry @Sophoa & @Ginfordinner, many people do not mind working from 8pm to 8am if it means they can change their life for a UK salary.)
@Mintjulia small world, I've also seen something outsourced to Romania. But, as @DelurkingAJ says, it is so clear when it comes from the outsource team there sadly.
The experiences of @Livelovebehappy and @user1471432735 give us hope, I guess that companies realise much is lost when outsourcing to another country. As @Newjez points out, it is hard to make it work. But the salary savings are clear and companies will continue to outsource.
@GingerScallop "I think the questions are who will be replaced and the scale." As you say, those roles that cannot be done remotely. IT and admin to start (including all support staff and any call centre work.) You'll be surprised how many roles do not need to be filled by those will access to city centres or even in the UK.
It will dip in and out of both in country and off shore until the balance is found.
@Crazycatlady2020 "How would it affect the economy if all of a sudden there was a lot less PAYE?" Economies will adjust.