Yes, the option of adapting EF lenses is certainly there, and all the more so for someone like me who already has EF lenses. However, for me, spending money on a mirrorless body just to use EF lenses doesn't particularly excite me. Sure, I'd get a mirrorless AF system (which has its advantages), but I'd also have to use an EVF (I still prefer OVF) and have significantly shorter battery life. Neither of those issues is necessarily a showstopper, I'm just saying that for me there are pros and cons. Something which would help convince me to spend money on a mirrorless body is access to "better" lenses. "Better" means different things to different people, of course. To me, "better" generally means smaller and lighter while still maintaining good image quality (and inevitably, price is a factor too). So, for example, if I shot Sony, I could get the Sigma 85 f/1.4 DN Art, which has excellent image quality and weighs only 630g. What EF lens can I get which can compete with that? The EF mount Sigma 85 Art weighs 1135g. The Canon 85 f/1.4L IS weighs 950g. Then you have to add 110g for the weight of the EF/RF adapter (130g if you go with the control ring version). If I went with an 85 f/1.8, the Sony version is 371g, while the Canon EF is only a little heavier at 430g (although 540g once you include the adapter), but from everything I've seen the Sony is optically a step up. I won't go through more examples here, but if you look at the lenses I mentioned in one of my earlier posts, you will see a consistent theme.
Am I obsessing unnecessarily over a few hundred grams here and there? I shoot for fun, and the reality is these days, in any situation in which I am likely to take photos, I'm almost invariably with a young child and perhaps a few of his cousins, carrying a bunch of other things in addition to camera gear, and with other people who care a lot if I remembered the snacks and extra nappies but most of the time don't care at all if I brought my camera (even if they like having a few nice photos). Smaller and lighter has become generally more important to me than it once was (although even previously I had some gear where smaller and lighter was important to me, because I carried it on multi-day hikes where I had to carry a tent, food, etc). So, while obviously none of this is critically important in the grand scheme of things (certainly a first world problem!), being able to move to lighter and also physically smaller lenses would be a drawcard for me. Using EF lenses with an adapter does not represent the same drawcard. And as I've said in a previous post, having third party manufacturers providing more RF lens options increases the chance that someone will make a lens which comes close to being the lens I am looking for. I'm very happy to look at the fantastic photos people take with lenses such as the RF 85 f/1.2L, and I know many people would love to have an RF 85L, but it's not a lens I am going to buy.