When the SandForce SF-2281 controller launched it was exclusive to the OCZ Vertex 3 for a few months, then after there was indeed a host of SSDs launched which all used the reference SF-2281 PCB design, and these drives were indeed all identical apart from their ID string. So no point on crossflashing those. You also can't crossflash these SSDs to an OCZ Vertex 3, as the Vertex 3 uses OCZ's own PCB which has extra channel muxing chips. That's why the Vertex 3 was the fastest SF-2281 based SSD for a long time.
Now vendors are using different NAND, some use toggle NAND, some still use ONFI2 NAND. On some SSDs they use async NAND rather than the more expensive ssync NAND. None of these will have compatible firmware. Now you also have the Intel 520 which uses it's own PCB design.
The only reason I can think of would be to try and crossflash to a Intel 520, as then one could use the excellent Intel SSD Toolbox. I can't think of any other reason to crossflash.
The main problem with any crossflash is.
1, You need tools to get at the firmware and modify it.
2, No one really knows much about any SSD controller, not even the vendors. So I have no idea where one would start.
Saying that crossflashing is possible, only a tiny minority would be brave enough to attempt it on an expensive SSD.