Some of the items that are ahead of iX now in bitcoin that I certainly would like to include are the prevention of fee sniping and the update that can prevent 'consensus forks' from using different versions of open ssl......
I agree with you that there's no need to pull added features from bitcoin. I'd like to see an update to the latest bitcoin tree with those features not included just to gain the security and stability fixes. Like the openssl item you mention.
An approach to do this would be to do the update then selectively disable the new bitcoin features. I don't know how intertwined they are though.
For the curious this is how I go about updating old clients to newer code, assuming the codebase is from an original bitcoin fork with modifications added on top. There may be easier ways but I've found it useful.
I add both the old repository and the latest bitcoin as git remotes. I find the common ancestor of both repositories using 'merge-base':
git merge-base commit-id-of-ixcoin v0.10.2
abcdef123456
I checkout that merge base into a branch and apply the ixcoin patches to that. It should apply relatively cleanly since it's close to the actual repository version:
git checkout -b test abcdef123456
git diff commit-id-of-last-bitcoin-commit-in-ixcoin-branch..commit-id-of-ixcoin >x.patch
patch -p1 x.patch
git add . && git commit -a m "ixcoin patch"
Then checkout the bitcoin version you want to update to and do a rebase:
git checkout -b ixcoin0.10.2 v0.10.2
git rebase -p test
This will start a rebase by applying all changes to bitcoin one commit at a time. If any clash with the ixcoin changes then it stops, asks for a fix, and lets you continue:
...fix files...
git add ..fixed files...
git rebase --continue
What this approach allows is to analyse the bitcoin changes that specifically impact the ixcoin code changes as they happen. I find it easier than trying to apply the ixcoin patches on top of a new bitcoin where files have been renamed and moved, etc. it's still a fair bit of work but you can see progress as it shows you how many bitcoin commits are left in the rebase as you go.
Once done, generate the final patch:
git diff v0.10.2..ixcoin0.10.2 >ixcoin.patch
This patch can then be applied to a clean bitcoin clone and renamed as ixcoin. There are probably other changes that would need to be made to fix internal global renamings etc but it's a process to get there.