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There is nothing really talking against adding more block positions - except that no themes will support these positions.
This means that the no. 1 question asked in the forums - if we add more block positions - will be "Why won't my [block position] blocks show up???"
We could even make it dynamic - add new positions on the fly... but end up with the same problem.
With XOOPS 2.2.3 a lot more information about each block is available to the themes - its block id, its instance id and its weight. With the weight, it is possible to accomplish what you have done (in theme: If $block.weight < 10 show block before content, else after)
Adding new block positions is something I have wanted for a long time, but we will need some "fallback" measure for a theme to broadcast which positions it has available and perhaps let it define a default block position where all the blocks that are positioned on positions not in the theme will be put.
All in all it is somewhat more than just tinkering with the possible block positions (big thumbs up for the work done so far, though - it's just that it ain't for beginners)
"When you can flatten entire cities at a whim, a tendency towards quiet reflection and seeing-things-from-the-other-fellow's-point-of-view is seldom necessary."
Cusix Software