They won't care that it's a US based 401k. I promise!
This is a huge relief - I've been worrying too much about the signal it sends to still be using US savings after moving to the UK, but it's clearly the cleanest route. Decision made.
If I can trouble you for a bit more perspective: the reason I'm so touchy about appearing to be "unsettled" in the UK is that I have to travel quite a bit for my job, 35-40% out of the UK. Generally speaking my husband can't travel with me unless we're on holiday (maybe 5% of that time). I know that this is a separate issue - time out of the UK - and not to do with my income or savings, but I still worry that they'll knock me back for appearing not to prioritise time in the UK with my husband vs. the US, where I frequently need to return for work (every 4-5 weeks).
I may have the opportunity to take a position in the UK that would earn in GBP, albeit significantly less than what I can earn in USD remotely, but I would have the same amount of travel in my line of work regardless. I'm likely over-worrying about the signals the currency is sending, but it's exacerbated by my paranoia that my travel outside the UK will hamper my application. I know the strict guidelines on days away don't kick in until ILR, but if there's anything I can do now to preserve the ability the keep our home in the UK in spite of my work travel requirement, I'll do it, including an effective pay cut.
Super grateful for any further insight.