As others have said, you should definitely upgrade to a BD player right away. They are quite cheap now, so you will not be out a lot of money for it regardless of what the future holds. And BD is a substantial upgrade over DVD, assuming you sit close enough to your HDTV for it to matter much that it is not SD instead.
Also, there is a very good chance that you will never need 4k. Most people, right now, sit too far from their TVs to see all of 1080p, so having 4k would be completely useless for them. For more on that, see the calculator here
, and the chart [and simplified calculator] here
. If you have 20/20 vision, if you sit only 8' from your screen, you need a screen larger than
61" to be able to see all of the detail of 1080p. Which means that there would be no point at all in a smaller 4k screen at that distance for someone with 20/20 vision. At 10', it would need to be larger than
76" for you to see all of the detail of 1080p (again, assuming you have 20/20 vision). Of course, if you have better vision, then it would be a smaller screen at such a distance, and with worse vision, it would be a larger screen at such a distance.
My guess is that a lot of people are going to buy 4k TVs because they clearly see a difference in the store from 3' away, but they will put them in their homes so far away from their viewing position that they will get absolutely no benefit whatsoever from having 4k instead of 1080p. Which means I expect a lot of people to be wasting their money. But they do that now in so many ways, as most people spend too much on electronics, and not enough on speakers, if actual sound quality is the goal. So, of course, I expect that they will waste money on video gear that does not give them the best performance for their money, too.