As above, you have to ask yourself why it seems like Dev Markets ex UK makes sense. Because as soon as you start feeling that, there's a serious risk that UK and/or EM stocks have become much more attractive.
That's the basic mechanic of markets. Discount the obvious and bet on the unexpected. And the obvious is very often what we feel as passive consumers of media and observers of recent market trends (which we extrapolate out forever, as if the performance of US stocks over the past 20 years is a lesson, rather than a landmark of a particular era).
I don't think fees are a real consideration, once that low. The way a fund's managed, its tracking error, size, tax implications, etc. would tend to take over by that point. The way you hold and trade it. Even the promptness of receiving dividends might be a comparable rounding error. But the risk of missing out on over 50% of the planet, in terms of exposure, and that 50% being the fastest growing, youngest demographics, etc. could be a mistake ... There is an argument for just holding the S&P500, but I think the alternative is to hold the world. Europe's the potential basket case you could justify lopping off. EM's a riskier thing to bet against.