Some classic DSOs did real time trace updates, e.g. HP 546xx. (I don't recall roll mode on the '00B, but maybe others in the family did.)
I take the opposing issue against Tek's contemporary offerings (TDSxx0): on long timebases, they default to roll mode, which makes it impossible to measure signals visually! You must change the trigger setting to get a stationary trace; and even then, it only updates after a complete acquisition, not in real time. (Surely they could've done both, but, alas, these scopes are smack dab in the middle of Tek's terrible interface years. Whereas the HP 546xx's are a pleasure to use, to this day.)
Tim