A plan sponsor has approached us to do an illustration for a DB/DC combination of plans. They had previously met with a firm who discussed with them "backloading" the plans with almost $5 million in contributions to make up for the last 25 years of not contributing. For the life of me I can't remotely think what they might have been thinking about? Does anyone have the slightest idea what they might have been referring to with this comment?

Wow! Sounds like someone thinks the NC can include prior service cost. Probably not. Certainly, the benefit formula can be backloaded, but that word appears to have a different usage in your question.

However, a better analysis would include more facts:
how many partcipants are included in this design? relative number of HCEs/NHCEs? what type of formula? how many EEs are at the max?
Etc.