Filling out immigration forms by hand is pretty old fashioned anyway. Some countries have done away with them as an archaic waste of time and paper. I mean, does anybody really read them, other than the immigration officer who may or may not give it a perfunctory glance while scanning your passport? Customs should be you either declare your stuff at the red channel or take your chances being spot checked going through the green lane or whatever the local equivalent is.
A better way to do it is to offer an online version, kind of like an ETA but without making visitors pay for filling out the form like an e-visa. Or hand out the cards at the check in desk or at the gate so people can fill them out before they board.
I will probably have a pen with me in the overhead bin, but it is a pain sometimes to get up and get it, fit out the form, then get back up and replace it in my bag. Even more so if I'm not in the aisle seat and I have to make someone stand up twice so I can get it.