LJ wrote:If you've to pay GBP 10 for single entry in the UK (which is one of the proposals for EU nationals) then I would reckon you think twice about a weekend trip to London. Moreover, you cannot just "pay" the fee at the border, but you need to apply beforehand. How many people will "forget" this and AFIAK ETIAS will not provide an alternative whereby it can be arranged at departure. Maybe it will not influence people going to Spain or Greece (as there is no alternative where you've good weather in Winter/Summer), but there are alternatives to a weekend in London or Edinburgh.
As for proof, the tourism industry isn't very pleased with ETIAS. It points to ESTA where the US government used the funds from ESTA for US promotions in order to offset any negative impact from the implementation of ESTA. Unfortunately it's difficult to calculate any impact (especially when you introduce mitigating policies at the same time), but apparently the US government didn't think that ESTA would promote tourism to the US.
I would hope that any UK system would be completely reciprocal with the ETIAS in terms of cost and length of validity.
The only proof would be if there was a measurable drop in tourism after the introduction of ESTA. ESTA cost $14 and is valid for two years. Just about the only part of a trip to America that's cheaper than that is my morning coffee. The cost of ESTA is an insignificant addition to the overall cost of a trip to the US from Europe.