Hi Matthias,
I a patch would be welcome. I only need USB and SPI flash for my application. And USB was easy to setup. Currently I am also jiggling around the SPI / SPI flash support.
For USB, all you need to do is to configure it in and to copy Marek's clock setup in board_early_init_f for m28evk_config into your own config. Make sure you change SSP2 into SSP1, because the m28evk module uses a different SSP2 for it's second MMC controller, whereas the FreeScale mx28evk board uses SSP1.
To store your environment in MMC, you still need to patch board/freescale/common/sdhc_boot.c to make sure it's stored at the correct offset. You can find this patch on this mailing list. Without it, saving your environment will overwrite the MBR/ptable and you board won't boot next time.
But there is still the difference that I can download 2009.08 + imx-bootlets via USB (sb_loader). This does not work with the recent u-boot-imx repo and the generated u-boot.sb target.
I don't know why that doesn't work, but I don't have any experience there. Early this year I rewrote the broken FreeScale scripts to create boot streams, so I know a little about the way it works, but I no longer use those since the U-Boot tools do such a good job. You can have the scripts though.
Cheers,
Robert.