Income is a nebulous concept and everyone has slightly different twists in their views. I think form is more important than label. Here are my justifications.
Burning is not a separate source of income, it is a method of immediately distributing income from fees earned. I explained this in my previous post above.
Though one might theoretically claim transaction fees from BTS transfers as income to non-transacting BTS owners, it has no impact on valuation because it is not from an external source. It is only a transfer of value between owners. This is clear if you consider what happens if the BTS transaction fee were increased 10x. The net impact on BTS owners is that shareholders activity costs are now ludicrously high, offset by the increased benefit of periods of passive ownership. This is unlikely to make owning BTS more attractive for owners in general.
Increases in bitAsset supply, or increases in BTS collateral, are not forms of income, because they come attached with an offsetting obligation. Let me reiterate a case study I've raised previously. Suppose a company earns a fee from facilitating transactions between lenders and borrowers, where the sole purpose of the borrowing is to buy shares in the same company, and all lending/borrowing is collateralised also by the shares. Now while the company can claim fees as income, and growth in this business places a bid on the shares, the company has no claim on the collateralised shares. Those shares still belong to the borrowers and lenders, and there is a hard-coded obligation for their return should the business decline. They could no more claim this as income than companies in general could claim the funds raised via debt as income (or that brokers could claim their client's segregated funds as income). Yet, this product structure is effectively what a bitAsset is.
So taking into account some of the other points raised by others, I would say:
Income (distributed in the form of burns)
All transaction fees, except those charged against BTS exchanges
Any other fees related to UIAs or other businesses that might be established
Expenses (paid for by inflation/dilution)
I expect there will be strong differences of opinion, but that's at least the way I see it.