It's valid in every version from SQL Server 2005 to SQL Server 2014 inclusive. Probably in SQL Server 2000 too, but I haven't kept a copy of the transact-sql reference for SQL Server 2000 so I'm only 99.5% certain of that.

I don't imagine it will change any time soon. It allows more than 5*10**413 local temp table names in each connection, which should be more than enough for anyone, and anyway that number of identifiers would require rather a lot of storage just to hold their names in tempdb - a single connection using that many local temp tables many would use over 5.8*10**415 bytes of storage in tempdb just to hold the names, and that is quite a lot more disc (including drum and solid state) store than has yet been manufactured on our planet, in fact manufacturing it would require the use of more than 10**300 times as much matter as is believed to exist in our universe, let alone on our planet.