Got a chance to test out the RDP v7 client shipped in Windows 7 over Wine 1.3.19. The RD gateway (connect from anywhere) is the key feature i need but it seems it's supported in NT 6 (at least 6.1 for Win7) and later.
Configure the OS version to Windows 7 with winecfg does not help, or maybe worse, as all I got is the error complaining missing .MUI files even the .mui counterparts of mstsc.exe and mstscax.dll were provided in the same or en-US, en-US.utf8 folders.
Feeding Wine with the .dll required by mstsc still shows no luck. Let's wait and see if later version of Wine could fix it or not.