I'm a little optmistic. w00t! 

Now we can have flamboyant colored light and cheesy particle effects in Q3!

...wait a minute... 

i'm more hopeful that this might open the door for adding q3 features to quake. 

seems like some engine mods already do that to some extent, what with md3, q3bsp, and 32bit color texture support. But a complete shader system and heightmapped alphablended terrain in Quake - well it would be interesting for sure. People could either abuse it and make utter shite, or something utterly cool we've never seen before. 

I'm pretty certain the Quake Arena loading code for MD3's is quicker and more reliable than the code in current engines. It is funny how md3's load without a hitch for Arena on this craptastic machine of mine, but any more than a few static meshes in a custom Quake engine, and the redraw rate gets floored (I haven't tried the latest release of Dark Places and FTE on it yet, though). 

You win that one Lun. 

Q3Radiant is under the GPL and you can use it for commercial purposes without paying fees to ID. However this doesn't apply to GTKRadiant, did I get this right? 

take a look at the first paragraph of section O of the GPL agreement. GTKRadiant is a derivative work of Q3Radiant, so the answer to that you would think would be yes, it is covered. But look down a little further, and you encounter this:

These requirements apply to the modified work as a whole. If
identifiable sections of that work are not derived from the Program,
and can be reasonably considered independent and separate works in
themselves, then this License, and its terms, do not apply to those
sections when you distribute them as separate works.

Now, it depends on the semantics of what is reasonable. Let's take a hypothetical case using the Q3map source here as an example; suppose that Ydnar's addition of phong shading to q3map2 used someone's method of phong shading who got a patent for that method? Then we are SOL and would have to use q3map. Not an unreasonable case, btw. As you'll notice in the readme, Id had to seperate out the Jpeg library stuff.

So, the answer is, it depends. 

What's more confusing is this: GTKRadiant is a derivative work of Q3Radiant, now that Q3Radiant has changed it's licence to GPL does GTKRadiant fall under the GPL (per GPL's provision)? This doesn't really make sense to me.

Say I created a piece of software and licensed it's code for commercial exploitation to you for a big amount of $$$. Now I relicense my original piece of software under the GPL. I don't think I can now force you to GPL your commercial derivative: my license change cannot possibly retroactively affect you because it happened after the code split. 

When the Quake2 source was GPLed, the mission pack sources from Xatrix and the like were not since they had a prior contracted agreement with Id. So you can use the original Q2 source to your hearts content in a commercial project but the add ons you cannot (the game .dll for Reckoning has superior AI code, for instance). 

Wonder if there'd be a proper Q1 sequel done in Q3. 

From q_math.c, Q_rsqrt():
i = 0x5f3759df - ( i >> 1 ); // what the fuck?

Always good to know that the engine coders don't know what is going on. 

hard coded like that, that is odd. Might as well be switching circuits with on and off toggles the old fashion way than to bother with code at all.