Note: This is a tax idea for next cycles government.
Vertical integration in WT still poses a problem for the economy, the purpose of this idea is to not solve it as per say, but to help mitigate part of the advantages.
So, the plan is to create a table of all the skills and which skills vertically integrate (significantly, not just one recipe), so for example Mining & Smelting would count, but basic engineering and mechanics would not (as only the iron wheels is from BE, and this is such a small part of the market). Some work would have to be done to decide what clashes and what doesn't.
This would then act as a sales tax multiplier. If a player or company has a VI skill set, they would pay 50% higher sales tax (example figure), than a non VI player.
The theory behind this is that the increase in tax revenue would offset slightly lower sales taxes overall, but those not VI would still result in similar or higher tax levels, as more trades occur.