Issue: Basing this instance on the ability of a set, idealized group, instead of a random group of players and classes, is a mistake, and unhealthy for server population. Other servers using high level instances made this same mistake which resulted in many classes and specs being completely eliminated from contention for slots, and a small segment of the player population actually running the instances with any regularity.You can expect to face new boss mechanics which require good coordination between the members of your group.
Recommendation: Create an instance that can be regularly and successfully completed by a variety of classes and specs common to the pick up groups that make up the majority of a server.
Issue: Favoring characters already equipped with decent gear and realm rank for a PvE instance is the exact opposite of what a PvE instance should be, as the instance should help gear out freshly created characters so they can then be more viable in RvR.It is also recommended that players are decently geared with some realm rank.
Suggestion: Rather than require players to kit out their characters and RvR so they can then be viable for a PvE instance, take the approach that the PvE instance will help their freshly created characters be more viable in RvR. If a greater difficulty level is the goal, then perhaps a scaling system could be implemented that increases the difficulty based on the average realm rank of a given group.
Other servers implemented high level instances, and while they were taken advantage of by some of the community, most of the community ignored them due to the unrealistic requirements needed to complete them. Entire classes were ignored for participation, and of those classes that were viable, most mandated a single spec in order to be accepted and effective. This resulted in the need to respec an acceptable class, or to create and keep an "instance" character for use solely in the instance / PvE. While those options are acceptable to some of the players, they make up a minority of players, while excluding the majority, and the goal of any shard should be to engage and maintain the majority of the player base, not the minority.