I would like to define what a Holdem Simulator might be, then to discuss ways that it could be used, and what it might be useful for. Of course the primary use must be to optimize win rates. So here goes:
My definition of a Holdem Simulator would have at least 10 parts:
A dealer. This is a program that simulates what a real dealer does. Deal cards, enforce rules, handle money, handle conditions such as All-in, split pots, and side pots.
Evaluator. This program would determine the winning hand. It would also determine made hands and draws on each street for every player. It would evaluate boards and assign a numeric value to the boards.
Players. This program would simulate all player actions using a Database. It would never make decisions to fold, check, call, or bet. It would only use files in the database for that. Ranges, Rules, and options.
Database. A collection of files that control all player decisions. For example, the ranges that all players are familiar with preflop such as open, call, bet 3, call bet3. Bet4, call bet4, all-in for every position. It would include ranges for things like MDF on every street. Rules that determine what hands a player will fold, check, call, bet, or all-in. Options for things like stakes, bet sizes, etc..
Editors. Specialized programs that allow for editing of all files in the Database.
Reports. After the simulation of a large number of games, many reports would be generated. Reports for hole card EV and hand EV on every street. Things like that.
Utilities. Many are possible. For example one to optimize the Database files for the best win rate including things like MDF ranges.
Hand Histories. No one will trust a simulator unless it produces Hand History files that can be analyzed by applications such as Holdem Manager or Poker Tracker.
Hand History analyzer. Simulation is of limited value unless opponent Strategies are accurate. That can be achieved by parsing real Hand History files from the website that a user plays at and for the same stakes.
Applications to assist during play. Teach. Have drills. Complete feedback loops.
Now for the discussion part:
If such a simulator existed what could it be used for?
Results of a simulator are generally close approximations. Is that a problem?
Are there other ways to determine an optimum MDF range?
Are there other ways to determine the EV of hole cards for every street?
What unique problems can a simulator solve?
Are Simulation and Solvers mutually exclusive?
What in the world is a simulator good for?
What would you add?