It sounds like if a user wanted to replicate a volume-per-bar (such as for a money flow index indicator), then this is what he will need to do:

* Set future brokercommand SET_VOLTYPE to absolute volume (either ticks or real)
* Therefore, future brokercommand GET_VOLTYPE will acknowledge this setting.
* User will then detect changes in absolute volume and use that as real volume or tick volume for a given bar.

Is this correct?

If so, I would definitely use the absolute ticks setting for any forex plugin and an absolute volume setting for stocks, options, and futures.

Question: Were you planning on adding these brokercommands to the IB, FXCM, and Oanda plug-ins?

I also understand that, depending on how the plugin collects history data, whether from newest to oldest or oldest to newest, that it might require absolute volume to be accumulated in reverse order. That is...
* Newest volume is zero
* Previous tick is higher
* The tick before that is even higher.

So you can leave that to the end user to straighten out. (Or I might publish a handy helper function or two in the headers.)