WRT patch 1 ("nsiproxy.sys: Get rid of echo request thread."), it doesn't look like the icmp sending part is supposed to be ever blocked for considerable time, so extra queue for performing send looks unneeded. That allows to return some types of failures synchronously (like Windows does) from the Unix side handling.
WRT "nsiproxy.sys: Don't try to check for original packet for ping socket.", ping sockets (both ipv4 and ipv6) are not supposed to receive unrelated packets (unlike raw sockets) and don't have original raw packet appended. In fact, those sockets do not seem to receive icmp error packets at all (probably because most of them are originating not from target host but from something in between), while maybe this part in theory can be improved in the kernel in the future.