growth is all the rage these days among startups. essentially how you can use tech to make products that market themselves in more predictable/ sustainable ways than just one-off product launches or paid ad campaigns. i've seen full-stack devs go into growth/marketing and essentially operate as a one-person team since they can launch and scale tests from idea to iteration. What's going on at reforge.com may interest you in this regard. It's applicable for both B2C acquisition and B2B lead generation.
another compelling angle to take is to get a deep understanding of applied statistics/ data science so you can build analysis tools or predictive/ML-driven features on top of the core products you're building. this might overlap with your existing skills quite well already, plus, it's growing faster in demand across industries/geographies.