It's mainly a psychological thing, the difference between f1.4 and f1.8. In some ways the f1.8 is better as it's smaller, lighter and with much less breathing with the biggest obvious difference arguably and at least I believe so being the difference in the size of the bokeh balls wide open.
I've never really warmed to the 55mm f1.8 as excellent though it is with a couple of provisos it's 55mm not 50mm. The other Sony and other marque options are the Sony 50mm f1.8 but I'm not going to even try that on my A7 as I'm convinced the focus will be pants and the much larger Sony and other f1.4's and the compact but f2.5 Sony G.
One thing I have thought of doing is getting the 50mm G and having the 24 and 50mm G's and the old 35mm f2.8 as my main kit with the 20 and 85mm f1.8's and 28mm f2 for those once in a very long time uses.
I do have the good Voigtlander 40mm f1.2 and the excellent 50mm f2 and of course the "interesting" 35mm f1.4 but I don't get a lot of chance to be out by myself these days and when with with someone else AF is better as I'll be quicker and not turning every trip out into a photography outing.
I'll end up just keeping what I have