As Valve has released a mini-SDK for plugin authors, we now can definitively make a statement about our Orange Box support plans. There is a lot to soak in, so I'm going to simply highlight the major points with bullets.
If you have any questions, please feel free to post here, or join IRC
>> We are going to release a new Metamod:Source version, 1.6.0, within the next few days.
>> Metamod:Source 1.4.x plugins will not run under 1.6.0. Recompiling and minor source code changes will be necessary (these will be documented clearly).
>> We are going to release two versions of Metamod:Source 1.6.0: An Orange Box version, and an "Original" version.
>> Metamod:Source 1.4.x will remain a stable, supported branch until Counter-Strike:Source is moved to Orange Box. This is so everyone can continue to run legacy plugins while Valve games are still running on the original engine.
>> We are going to release new documentation and new sample plugins for Metamod:Source 1.6.0.
>> A SourceMod port will probably take another week, as it is a very large project. We are going to distribute two branches: The Original branch will run under Metamod:Source 1.4.2. The Orange Box branch will only run under Metamod:Source 1.6.0.
>> Once CS:S is ported to Orange Box, SourceMod will only run on Metamod:Source 1.6.0, however it will continue to support both engines.
>> SourceMod plugins (barring custom SDKTools usage) will continue to work without a problem.
>> Even if Metamod:Source 1.6.0 was backwards compatible, the HL2 engine is not, and thus C++ plugins on the original SDK will never work on Orange Box, and vice versa.
We hope that developers will continue to use the Metamod:Source platform as everything moves to Orange Box. Metamod's SourceHook has received major improvements that we are very excited to finally announce, now that we have the chance to break backwards compatibility.
(Note: This is as large undertaking, and we have put a lot of time and effort into it. Please do not nag us about when it will be done.)