as jsameer already wrote, dhcpd will be obsolete. Actually from 15.1X49-D60 (released 3 days ago) the dhcpd-configpart is hidden and a warning shows at each commit stating that you should convert to jdhcpd config.
15.1X49 is for the new SRX300 series, 550M and 1500 so I don't expect this behaviour to be put into 12.1X or 12.3X for the legacy SRX200 series... so as long as you have your SRX240 then you are not forced to change DHCP daemon :-)