This is an interesting design choice.
I'm sure the idea here is to reduce the number of abuse complaints directed to Cloudflare, but it also seems to significantly reduce the value of the service.
I'm excited to try WARP, but without IP masking, I'll need to keep paying for a commercial VPN service. If I'm already paying for a commercial VPN, I don't see why I'd ever use WARP.
That said, I definitely trust Cloudflare more than PIA/NordVPN/etc. Some more "bulletproof" providers like Mullvad are probably even more trustworthy, but I don't think Cloudflare is going to mine (or sell) my data.
At this point, I'm just not sure what use-case WARP would really fill for me.