I think that provable deep expertise in some niche is a pre-requisite to this kind of positioning. Is there a market for general purpose software consultants? Who is the target audience?
Certainly is, as indicated by the continued success of for Accenture, McKinsey Digital, Deloitte Digital, IBM, EY, KPMG, PwC, Aon Hewitt, and probably a million more smaller consultancies and agencies.
Its certainly a suitable career choice if you enjoy a mix of technical solutioning, ideation and development work across a range of clients, geographies and technical domains. The caveats of course being sometimes your skills stagnate or the work-life balance isn't there when comparing service-organisations with product-organisations. But, depending on where you want to build your career, this kind of work for those kinds of places can be quite an accelerator.
A brand's goodwill (trust and so forth) is a function of its ability to deliver success for the client. Success establishes that trust. People who run projects internally, and use consultancies or agencies, still have business requirements like any other team (whether internal or external). I can't imagine a team would be immune to scrutiny of a project failure (i.e. from shareholders) simply because they relied on a third-party. The same argument doesn't make sense if Amazon AWS suffered downtime, for instance?
I can't imagine a CTO or VP of Engineering turning around to a team that failed to deliver as a result of poor partner selection, and saying "nah, you're all good, we'll blame them." As blaming a third-party doesn't re-coup the millions in lost opportunity, shareholder backlash, press, etc.
Even if we assume that they are willing to part with stock for consulting engagements, can you afford to wait years to get paid?
Can you afford to pay taxes on that income this year? (to you it's paper money that might never to turn into real money; to IRS it's as good as payment in cash).
A number of startups really start having this issue once they start seeing some traction.
Maybe they're actively looking for new or additional senior technical leadership or just scaling the team.
Either way the opportunity is certainly there for companies to hire temporary technical leadership.
The problem here is once they have traction and funding, they likely have a full-time CTO. Fractional CTOs are generally needed at the seed stage when the technical solution hasn't really come together and they don't have this skill-set in house. They also don't have money. It's a slippery slope, and you're better off being a technical advisor (low effort, low equity, low risk) than working underpaid and overworked.