@Dylan Mathias Yes, it can be revoked due to several issues not being met:
1) The Qualified Opportunity Fund (QOF) has a 90% AUM test every 6 months. This means that 90% of the AUM must be held in qualifying investments such as 1) Qualified Opportunity Zone Property (QOZP) or 2) Qualified Opportunity Zone Business (QOZB).
2) The QOZB has a 70% AUM test.
3) The "substantially improved" test not being met. For example, the additional investment in a property needs to be at least 100% of the basis of the property (the building minus the land).
4) The property is not sold before Dec. 31st, 2048.
5) Capital gains must be invested into the QOF within 180 days of the gain.
6) Funds from #5 must be invested into a QOZP/QOZB within 180 days. However, there is a 31 month safe harbor for working capital for QOZB. Meaning, funds could be held in a QOZB for 31 months before having to pass the 70% AUM test.
Those are most of the main considerations to be aware of to insure you do not lose the tax advantages.
***Also, Dec. 31st, 2019 is the deadline to have capital gains invested into a QOF if you want the 7 year step up.***
As always: I'm not a CPA. This is not tax advice. Consult your CPA and attorney.