1. You can still use the native client against 6.5, but you can't set some of the new hardware versions. NBD, really. You can use the built-in web interface if you need to do that, which is getting better each iteration.
2. Not true, you can use the same ESXi free license key on multiple instances of the same version. Only real limits are CPU sockets and lacking the fancy paid features like powercli, vmotion, etc.
If there are costs associated with updating, perhaps, but that's par for the course if you want to keep using a paid version. You can't just pay once and use it forever, you have to keep the license up, hardware current, etc. If it's not supported, there's a reason. It's EOL in some way. It may function, but it's a problem waiting to happen.
We've really gotten off the track of the OP though, but you are spreading misinformation. If you want to run it that way in an unsupported and potentially insecure/unstable manner, feel free, but do not advocate others follow in your misguided path.