P: Export images at multiple resolutions in one go

I have discovered through experimentation that photos published to Facebook look best at 2048 pixels on the longest side (the maximum it supports) but images measuring 960 pixels on the longest side come a very close second so that's what I export at when Facebook.

I also publish the images on my own website, which uses SmugMug as a backend and is capable of automatically displaying delivering higher resolution photos (than Facebook) to the browser depending on the viewport size, so I export at 1400px resolution to strike a balance between filesize and image quality.

My problem is that it's not currently possible to export these two sets of images at the same time, I have to do them one after each other (because doing them in parallel is MORE than twice as slow due to LR's poor parallelisation of task execution), manually switching between different export resolutions and folders.

Instead, I would like to be able to pick two (or more) resolutions to export at, set (sticky) subfolder names for them (so that they end up in separate folders within the base export folder), and set LR to export all the images in one go. This would save me a huge amount of manual faffing around every time I export, and because LR would only have to fully render each image once (instead of twice as at present) it would dramatically reduce the total time taken to export both sets of images.

I realise that it should be possible to write a plugin to achieve this (and I'm looking into it) but surely exporting a set of images multiple times at varying resolutions is a fairly common use case (e.g. web/client DVD res and print ordering res for wedding photos) and it would therefore be of benefit to a significant proportion of the LR user base to make it worthwhile Adobe implementing it as a native feature?