I guess we'll see what RSG puts out after Under Defeat, but it could be Mushihimesama HD.
(not seeing RaidenIV(not out in europe), Radilgy or Shikigami no Shiro III happening, for some reason, but I could be wrong.)
we're far in this gen, but the 360 remains and will remain popular for quite sometime in europe (RSG) and in the us, so I don't see why RSG would not release DDP SDOJ if previous shmups release were profitable for them.
but as a reminder, if you really want Ketsui and/or DDP DaiÔJô on 360, it's pretty safe to bet that a jp system will remain the only way.
LeadenStride>I suppose the cheapest way is to find a good deal on a 2nd hand console on some boards. (like shmups sys11) or get in touch with someone in japan for when the system really dies of completely (hey, it's still moving...a bit

)
(or get a modded system from any region, if allowed in you country (tag words : RGH or JTAG)(flashed dvd drive modded system won't help))
I should add to that, that I got a jp system last year, and it's my only 360 (sold my PAL system) and my knowledge in japanese is ok, but not quite good enough for RPGs and such, but you should know you can find a lot of ASIAN release (from Hong Kong and Singapore) that are pretty much the american version but with asia/japan 360 region code

(also there's some places to find RELIABLE info on 360 region locking like
http://www.abgx360.net/verified.php (if you know how to read it) for example I found the other day that I can get a cheap PAL version of BlazBlue CS Extend and it play on my system with english text and is the same as the english asiaa release)