I'm not a fan of diesel fumes and either I'm becoming more sensitive to it or there are more cars shooting soot out of the exhaust than there used to be.
That said I wouldn't want to penalise anyone for running an older car. What I would love to see banned is any diesel, new or old, that is throwing visible smoke. There is no need for it if they are maintained properly.
DPFs are unfortunately now well and truly part of the cheap old banger sector of the car market and the general buyer in this market isn't going to spend hundreds on replacing a DPF when 'my mate Dave down the pub' will 'sort' it for £70. Unfortunately sorting it to Dave means smashing the guts out of it and installing some OBD bodge he has no clue about but his mate Bazza tells him is pukka.
No smoke no poke types who wear there sooty rear ends, from dodgy remaps, with pride simply need their cars crushing.