4) a bonus paid at time of exit will be subject to regular income tax, while options can (but don't always) benefit from long term capital gains tax.
Rough example: if an employee were to benefit to the tune of $1M due to sale of company, under this system, they would be taxed in the highest bracket, at 39.6%, plus FICA withholdings, so they'd end up getting less than $600K from the sale. If they had options instead, and had held them for at least a year, they'd pay 20% in capital gains, so they'd walk home with $800K.
Your plan is costing your employee $200K+ in this scenario, with no commensurate benefit to the company.
If you don't want to give options, why not do profit sharing instead? Let current employees who have been with the company longer than 1 year enjoy some cut of the profits each year the company has them?