You have the skills that founders need to succeed, but you don't want to work for free, or forever. Invest some of your time now to win new business and earn upside when the founder succeeds.
Decide what % of your fees to invest, at what multiple, and for what % of revenue. Avoid the complexities of equity and valuations, and defer taxes until you get paid.
Invest some of your current capacity in promising founders. Create a portfolio of investments that will generate future cash flows. No waiting 7+ years for an acquisition or liquidity event.