I've pulled the trigger on the Dell this morning My reasoning is that it's the best available now and it's at a comparatively good price.
I don't want to wait till September for this LG monitor as I'm building a Ryzen ITX for my gf (a teacher) for the summer holidays with some of my old bits and that includes my existing 27 inch monitor. I could just use the TV in the interim and wait for the LG but that Dell deal, with good QC and support, seems too good to pass up at the moment.
Any buyer's remorse will likely be tied in to how the UW5 panel improves upon the UW4, and at what cost, but buying now... The Dell is the one (in my opinion).
For others, if waiting is no problem, I would wait to see what this brings and if LG respond favourably to the market with competitive pricing.