AP

I believe that what you suggest is more appropriate to trades than to positions. I don't know if it's been discussed somewhere, but it would be good to separate the...

How about having a class Asset as a base class, then Stock, Future, Forex, Option, etc. inherit from it? Similar to what Quantopian/Zipline does. P&L and slippage calculations are based...

Isnt't the hedging system just a specific view of the trades (group by something)?

True. So as long as tags are attached to trades, it's possible to build custom views.