Costly. I'm not sure if you could do block sized transactions that would take upwords of 10 minutes to verify though.
Discussion
This is the Bitcoin Talk conversation from 2013 and the attack has been improved upon since then.
Also the GitHub issue which is closed without a solution, relying purely on miners to not mine non-standard transactions such as these.
Thanks I'll take a look.
Attack vectors like thee exist and dum dums want to ossify 🙄
the having your cake "noooo we can't hardfork that would make us heccin centralized" and the eating it too "here's a list of valid transactions that I hate and should be super duper invalid" attitude of an irrational useful idiot person. but you can easily change their mind by making enough funny image macro spam about it.
Lol. Followed.