I expect they'll make tweaks, but I doubt it will look totally different (too bad, because a more ala carte or points based system might be interesting).
As to how it HAS worked... it's an add-on option to a resort stay, and is tied to the number of nights off your stay (e.g., a 2 night stay would get 2 "days" worth of credits per person on the reservation). All guests on the reservation must get the plan, or none at all, and it's for the full length of stay. Credits are available from the time you check in until midnight following the morning you check out.
The various tiers of the plan have different credit allocations, for example the quick service plan includes two counter service (CS) credits and 2 snack credits per person per night, whereas the regular
Disney dining plan includes one table service (TS), 1 CS, and snacks per person per night. All credits are awarded in a lump sum and can be used at any time - if you wanted to do three TS meals in one day, that's fine, you'll just use up 3 days worth of TS credits to do it; the credits are also awarded to the reservation, not to individuals, and can be used by anyone on the reservation at any time (so make sure you coordinate with your party!)
A snack credit can be used to get a snack or drink at participating locations, eligible items are usually clearly marked on the menu. In general, a single-serving non-entree item usually counts as a snack.
A CS credit can be used participating locations to get an entree (or a combo like a a chicken tenders basket with fries) and a beverage. A TS credit can be used at participating locations to get an entree, dessert, and beverage - OR selections from a fixed price menu (where available) including beverage - OR admission to a buffet or family style meal, including beverage. Some restaurants are "signature" locations and require 2 TS credits per person for the same entitlements (just at a theoretically better quality and experience).
A "beverage" is single serve fountain drink, tea, coffee, juice, milk, smoothie, shake, or (as of recent years) alcoholic beverages from the standard menus. Refills on drinks normally eligible for refills when purchased are included. Drinks coming in souvenir cups, wine flights, etc., are excluded.
You cannot split entitlements, e.g., you can't use a CS credit to get an entree and then go somewhere else to get a drink later. Use it all or lose what you don't use.
The dining plan is a payment method, like cash, credit card, or room charge - at the register (for snack/CS) or at the end of your meal (for TS) you will pay with credits and covered items will be zeroed out on your check, allowing you to pay for any non-covered items through other means. Gratuities are not included except in rare cases where they are specifically listed as included; taxes on covered items are included.