At last an interesting thread....
I will install the DPF emulator over Christmas, I waited until I pass the NCT here in Ireland. That was done last Saturday and the car passed with not a single issue.
Another good mod is the sprint booster, I have one installed for almost a year and it helps alot with the turbo lag until the engine reaches the 1800-1900 rpm.
For the people that don't want to do a dual exhaust conversion I have test fitted a backbox from the old 2 litre petrol IS200 and it fits the IS220d like a glove. I'm planning to buy one of e-bay or a scrapyard and remove its guts and then fit it on the car. I believe that a high flow exhaust system will help the turbo spool faster to some degree.