It seems to me that if there’s any delays, fast London services can cause trouble stopping in platform 3. In some cases, there have even been nonstop services running through platform 1 or 2 while something else is in 3, which I believe has itself led to incidents with trains being too fast over a crossover at the north end. So how about routinely sending stopping intercity services into platform 1? Thameslinks can use platform 2 all day, and morning Great Northern services can quickly get in and out of platform 1, as they’re just picking up passengers. Anglia terminators can terminate in 7 and depart from 6, making use of the shunt as a turnback. Thanks to the Werrington diveunder, Lincoln services can go into Platform 5, retimed to not interfere with any intercity services potentially requiring 5.
Either way, it’s not impossible.