The point of an IP4v2 (to borrow your naming convention) address is that because it's prefixed with an IP4v1 address, then it can still get somewhere useful if

The point of an IP4v2 (to borrow your naming convention) address is that because it's prefixed with an IP4v1 address, then it can still get somewhere useful if an intervening router or even the destination gateway doesn't understand IP4v2. Think of IP4v2 as essentially embedding a NAT field into the IP header. This might work or it might not in any given circumstance but the path to make it work is a lot more straightforward. As for the routing table size issue, it's not really an issue at all. Assuming extra octets, a /24 block holds 16M addresses instead of 256 (or 254 realistically). You don't need a larger routing table. This would also allow an organization that might've had a /16 or /8 block or multiple blocks to get by with 1 (or a few) /24 blocks, allowing you to reclaim blocks without making external routing tables any larger.