$1500 is about my limit for a lens so I'd like to see a higher quality 75-300 f/5.6 Pro with Sync IS. Or maybe a 50-200 f/4 Pro with Sync IS.
I actually find the 75-300mm to be fairly usable.
I had a fall in March, and I cracked two vertebrae and I went to have lighter weight versions of my lenses. I got the 75-300mm to be a lighter alternative to the 100-400mm f/5-6.3 mark I lens. I've now shot with the 75-300mm more often in 2025 than I have with the 100-400mm lens (85 shots vs. 74 shots).
Sure there are times when the 100-400mm comes out due to focal length or splash resistance. If OM was to come out with a splash resistant 75-300mm I would seriously consider upgrading, assuming it is priced similar to the current 75-300mm lens. While Sync-IS is nice, it isn't critical to me.
At the same time I bought the 75-300mm to be a lighter weight alternative to the 100-400mm lens, I bought the 40-150mm f/4 to be an alternative to the 40-150mm f/2.8 lens. That lens hasn't gelled with me. Instead I tend to use my 12-200mm f/3.5-6.3 or 14-150mm f/4-5.6 mark II lenses for the 41-150mm niche.