What is the meaning of the Bitcoin address version?
Last time I heard of it, the future of version bytes was still unsettled.
Currently, they are used to force incompatibilities between several base58-encoded data structures:


addresses / private keys
testnet / realnet
alternative-chains variants (namecoin etc…)


This way, you cannot misuse one for the other.

Someday, it might also be used as a real version number (the current SHA-256 + RIPEMD-160 + base58-encoding for keys could become obsolete).