Firstly, just to say thank you for such awesome software. I’ve been using siril for a while. I recently started a PixInsight trial period and have been A/Bing some processing with PI and siril - results, at least for my setup, are actually in favour of siril except in a few cases. Certainly sufficiently so that I think I’ll be saving myself the cost of a permanent PI licence 
Here’s my wishlist item (and it’s something that PI doesn’t do either). When imaging with a Newtonian we have to deal with coma. Mostly it’s corrected by my coma corrector but if collimation is a whisker out there can be some residual aberration resulting in elongated stars near the corners.
I came across this tantalising web page outlining an approach to deal with it using deconvolution: Correcting Coma/Field-Curvature Type Aberrations With Deconvolution
Essentially the process is to measure the psf length, width and angle of a selection of stars at various points throughout the image and then use these measurements to identify the central point of the aberration and parametrise the psf as a function of radial distance from that central point. A deconvolution process is then carried out, but at each point in the image the psf used for deconvolution varies according to the measured parameters.
It sounds like a neat idea and the example images on the website certainly show that it delivers some improvement. Unfortunately the only implementation of it is for ancient versions of AstroArt.
It would be very nice if Siril could implement a process like this, as far as I am aware it would be unique among current astro processing software.