There's the conundrum. If you make it easier to qualify for disability benefits, then the cost (premium) increases. If you increase the payout amount, then the cost (premium) increases. There are some efficiencies that can be achieved in the shift to a public non-profit insurer and compulsory coverage, but that only gets you so far.
In my view we (Singapore) ought to "bite the bullet" and just get it done. Change the benefit qualification rules to "2 out of 6 ADLs" -- relax them at least that much -- and increase the payouts to $1,000/month (2018 dollars, automatically adjusted annually for elder inflation). Coverage begins from birth and with no pre-existing condition qualifications. Payouts are treated as ordinary income for income tax purposes. (Almost nobody would actually owe income tax on benefits, but most well-to-do individuals would. That's fair. Income tax collected on benefits would be earmarked and plowed back into the program.) Make the program compulsory, and provide premium subsidies to lower income citizens. Premiums start from age 25 and end at age 50, 60, or somewhere in between. There's a transition program for older Singaporeans to get into the new "DisabilityShield Life." There's no 72 month cap on benefits. Benefits last as long as the disability lasts. There is, however, a 3 month waiting period before benefits start, so short-term disability is not covered. (There's room there for an "Integrated Disability Shield" private sector top-up, plus a monthly benefit amount top-up, for those who are interested in buying up.) Benefits are coordinated with a (subsidized, if necessary) CPF LIFE Escalating Plan cutover at age 65.
....And that's that, done and dusted. Yes, it'll be "expensive," but disability plus poverty = major suckage. Let's just do it.