Unfortunately, there are still a lot of people who don't want to take it, with comments like I don't need it as I'm not planning to travel oversees (a few taxi drivers gave me that excuse), not to mention the paranoids.
If only there was some benefits, that people felt more, like restaurants that only allow vaccinated adults, or shorter time at quarantine hotels etc. Technically with the tracetogether that connects to your IC number, it shouldn't be that difficult to implement. Then check-in it would accept the check-in for vaccinated only or something similar.