Their have been rumours and hints and lots of "soons", that said even if they do launch in the UK you may want to wait a few months for them to solve their teething issues.
Braintree which have an amazing reputation in the US, when they launched in Europe did so with their support still in the US, prices on demand and with paperwork requirement not even a bank would ask for to be emailed to them. Other then the support and pricing the other bits were sorted out quite quickly but for the initial customers the setup and initial period was a little choppy.
That said now I would wholeheartedly recommend Braintree in the UK based on a couple of clients more recent feedback. I suspect when Stripe launches a similar scenario will occur, so for them other then regulatory issues, I suspect the biggest issue is getting the support infrastructure in place, trained and modifying their processes to deal with different regs, as much as getting approvals and bank backing.
Where possible I will use AMEX for all my personal transactions mainly as I have a longer interest free period on spends making budgeting easier, also while its a pure perception thing the few times I have had the need for a chargeback or had a problem with my card its been resolved in minutes.
Of course as a merchant it's higher fees, has weird conditions attached to it and virtually all AMEX users have another credit card (indeed Amex provide me with a visa card for when I can't use my amex) so there is little benefit to supporting amex.
We began to look at them, unfortunately while the API was straight forward the documentation was simply wrong in many places and contradictory which was a tad frustrating. The biggest issue for us was they simply couldn't answer even the most basic question like their current PCI-DSS status, information about their network or datacentre setup (or even where it was hosted) in effect we couldn't complete any PCI-DSS assessment docs. Needless to say, we simply did not feel confident handing over our companies account and other details they were asking to go live with. Let alone let them handle our payments. This was a few months ago, and they were having teething issues which may have now been resolved I suspect given how common such questions should be they now have the answers in place we may well relook at them in a couple of years time if they are still in the marketplace.
PCI Compliance is about a business not a process being compliant, while your solution reduces the scope of compliance it does not mean the business can just ignore its responsibilities. They still have to go through the motions just the emphasis is on you rather then the business. Which means your own documentation should be clear on what process are compliant, who did your assessment etc. So this can be then used for your merchants when doing their own assessments.
You may wish to change some of your terminology to match the rest of the industry a "reclaim" for instance I assume you mean a chargeback. You also mix the terms reclaim and refund in several places. Assuming you meant chargeback then a chargeback and a refund are two very separate things.
Also as pointed out the FAQ states only Euros are supported, I'm glad to hear that GBP is also supported I shall have another play in a bit. But how then is currency conversion reconciled?
Ultimately the site is littered with mistakes (mostly I'm sure due translation) and these reflect an image of service that's not quite finished.
The UK process (at least when we investigated it) and I assume the rest of the recently added countries is still very much send us more paperwork then a bank ever will ask for to a black hole email (or sftp) at Braintree and say a pray.
This is no worse then any of the other payment processors in the UK but hardly the frictionless option that is in the US.
While I applaud any move to bring more payment options in Europe this is really still very german focused and appears only half baked. The English documentation is interesting with lots of muddled terminology and when you start the application process bit's of it are still in german in places. The site also seems to lack error and confirm messages (wondering if this is simply not translated)
For those in the UK jumping for joy at a Stripe like payment gateway there is a bit of a gotcha it only supports Euros.
Also there is no details about who is actually processing the payments and several interesting and dubious (but again could simply be translation problems) statements about PCI compliance on the site which could make due diligence interesting.
Something to watch, but for UK merchants I suspect it may be a lot of work to get going so not quite the frictionless option people are holding out for. Be interesting to hear from a German companies perspective to see if similar issues exist on the paymill.de site?