Also, it's probable that Darkbasic Pro isn't near as fast as Blitz. DarkBasic sure wasn't. I highly doubt that the guys that wrote DB Pro became pros at designing 3d engines overnight. I suspect that DBPro's 3D engine is similar to Dark Basic's, with new additions and some slightly different syntax.
That really depends on the system and the display mode you use. I find DBP faster, others find Blitz faster (remember that the 3D engine has been completely rewritten since release).
Pixel / Vertex shaders are complicated to add full support for, because they require very low level 3D data access (to the world / transform matrices for example). With next gen shaders (HLSL / DX9) it gets even worse. Plus you need to cater for cards that don't support a given version of shader.
Blitz would need a whole host of low-level commands besides the shader ones.
I would think it unlikely that shaders will get added to B3D, although they probably will be in BMAX.
It isn't a matter of picking up a shader and plonking it into the code either - if you wanted to write your own you need a good understanding of assembly (and C for HLSL shaders)
To be honest, the cube mapped water is probably your best option - Unreal II uses it!