Pre-covid, easyJet did nightstop some LGW based aircraft downroute. The thing is, does the IOM need it? Admittedly, with an earlier LGW-IOM, the return into London can still arrive at a respectable time.
One of the easy nightstoppers was INV and that was subsidised in some way I believe. So maybe the IOM government could step in.
A frequent service is valuable to an island such as IOM but I am a little dubious as to the widespread demand for day trips, particularly these days. It’s almost a romantic view.