You're taking on market and execution risk here, for which you are not receiving compensation. (Presumably you set your consulting rates high enough such that engagements are a win for you. The SaaSification option is at a discount to your rate, which you only make up if you sell it to other people. "Selling it to other people" is often much, much more difficult than writing working software.)
Any consultants in the room who happen to have an engagement which would create usable IP could consider the following alternative: "You pay our normal rates, and you pay for hosting/maintenance, and we own all the IP." This is actually very common, because most customers of software do not want to get into the software business and hence they don't give a fig nutton about commercial exploitation of this system they want to buy from you. No purchasing manager at the US federal government is going to nail his promotion to GSWhatever if he preserves the government's call option on starting a SaaS starttup.