Maybe I should clarify what I mean by "upper bound". "Upper bound" means "how high could the number go if parameters X, Y, and Z are allowed to vary", but neither of us specified what X, Y, and Z were. The hypotheticals I was considering were "suppose the startup community all acted in unison towards increasing the number of startups". For instance, if the startup community exerted enough collective pressure, we could plausibly get Sarbanes-Oxley loosened, or force VCs to become more technically competent, or make it easier for founders to immigrate. But we can't just decide to increase how profitable it is to learn to program or start a startup; these things are driven by consumer demand.