A single EU VAT rate would be very harmful because no gov would be able to boost consumption by reducing VAT rate, it would also force small business to collect VAT as soon as they sell their first product.
What exactly would be the argument for allowing individual small governments to play with their economies like that? The risk analysis gets completely skewed by the fact that the EU implicitly backs the economy anyway. That just sounds like a recipe for another Greece.
The EU implicitly backs Eurozone countries because it has to, the UK is not a Eurozone country. The UK should definitely be able to control it's own taxes, the only alternative is fiscal union.
Sorry, I heard "Single EU VAT" and assumed you were talking about the Eurozone. Unifying taxation in the absence of unified monentary policy makes no sense to me anyway, so sure: I agree then. :)
I'm not sure how your conclusion follows. Why would having a single shared VAT rate imply that you couldn't have a minimum threshold before VAT registration is required?
If anything about VAT is going to cause grief for small B2C tech businesses in Europe, it seems more likely to be the changes affecting them from 1 January 2015 precisely because the VAT rates in different European countries are different.