My sense is that it's a low priority for the govts of both sides.
For Sg, the priorities are housing prices, domestic transport, foreign worker congestion, cpf etc. The PAP is already gearing up for next GE. The RTS will only get higher priority if a significantly larger number of voters see travel to Johor as an important quality of life marker (eg. as a means to a quick respite from the stress of Sg) and demand the govt provide better infrastructure to resolve the border congestion in the interest of a better work-life balance. I believe the number of S'poreans in this group is either not large enough to be heard, or they are not making enough noise to be heard.
For My, it's more complicated as it involves the federal and state govts, but more importanly the politics. The My govt (especially after the erosion of support in the last GE) is currently focussed on maintaining or even increasing support among a certain target group of people who comprise its traditional support base (you should know who they are), and this group does not from my observations form the larger group of users of the broder crossings with Sg and may instead even oppose closer cooperation with Sg on arguments that their customary rights may be overrun by foreigners etc etc etc...