Why HAM6 is not feasible from my point of view:
Well, if the proposed Amiga Video Format draft is taken into account, due to the way HAM works, in an attempt to move an image around the screen (such as subtitles, timing info, etc) will generate noticeable fringing that will degrade the quality of the image a lot. This is typical behaviour of an Amiga in HAM mode trying to move a blitter object around.
Also it has restrictions on color combinations between adjacent pixels that can only be avoided with careful planning and a few neat tricks. So I think no.
Changed my view on EHB:
While not present on the very first few A1000 NTSC models sold in USA and Canada, it sure provides 64 colors, so it could be implemented provided the player program checks that the EHB mode is available, and if not just ignore the offending bit and play the video at 32 colors. In this case we have to be carefull on datarates, which will obviously raise.
PAL screenmodes & support:
In an ideal world, PAL amigas should play PAL videos, and NTSC Amigas NTSC videos, but then, it is not an ideal world. So either the supplier of those video files generates two different versions, one for PAL users and another one for NTSC users or we just create a player capable of converting the formats back and forth between these standarts. While the last approach may seem the most reasonable one, an Amiga is doing much of an effort just playing the AVF, so convertion of formats it is not advisable.
My approach is the following one:
The screenmodes I described in the AVF are NTSC but can easily be adapted for full PAL use by any of the known popular methods, such as for example, adding blank lines. So in this case there is no image degradation, just not full use of the the entire screen height and a very small amount of processing power to generate blank lines to fill the screen.
I dont do it the other way round, because it means you either have to resize the image down, or cut the picture, which means either quite some cpu overhead or bad image quality due to image chopping.
Another thing against native PAL resolution sized videos is the fact that we will raise datarates even more.
While many argue about the methods involved in actually displaying the images and its feasibility, i may suggest we leave this task for the developer, so that he/she may choose his/her own approach, as there are many ways of accomplishing the task.
And i nearly forget!
A600 can have fastmem without acceleration, just plug one of those PCMCIA 16bit ram cards. (from 1, 2 and even 4 MB.)