I will agree with Frank - I personally don't think there be a next holy grail. No new release is guaranteed to be 'exclusive' and nearly all of them are worldwide releases.
It takes something very 'special' to become a 'grail' steelbook and to command a very high price. There will be steels that will gain some value over time. But to generate a huge price tag, and with all the mountains of re-releases and general releases, sadly I don't think there is going to be any.
In regards to some mentioned here, IMO they willl definately will not be grails. And yes I am being impartial because I own these and would love the value to rise!
- Terminator Korea: although very limited, it is a worldwide release steel and has no inside artwork. The slip is a J Card and not like the Taiwan slips which make it much more appealing in the likes of CA TW and T4 TW. The steel itself is less appealing to spend hundreds of pounds. Demand for this has dropped.
- Lawless: great steel, nice de-bossed bullet holes, the movie is not a hollywood block buster type movie to demand a big interest, regardless if it has nice de bossing or not. Many collectors who only buy movies only if they like the movie will pass on this so demand is less.
- Iron Man Play.com: This steel has a potential to rise slowly. With the original IM FS released and original grail, it is difficult to see owners letting go of the FS one to create more demand for Play.com one. Play steel has been hovering on bids for around £40 - £45 for a long time and the FS one has increased in value. The FS is believed to be around 8,000 made where the Play.com one is 4,000. As you can see the Play version has only half but it is still generally available on forums and on ebay. I'm not going into get into the full details of FS vs Play.com, I've explained that are the IM FS thread. If Play wants to become a grail, it has to topple the FS version and I don't think that is going to happen. There won't be two IM grails.