Looks like rules for the Ghostkeel just dropped and, out the gate, it seems quite reasonable:
Breaking it down, here are my first thoughts:
1 – Mobility — As a Jetpack MC, it can Deep Strike and use Jump-Shoot-Jump to either shoot and get back in cover or shoot and then move further upfield, so that is solid. We are not sure if the Ghostkeel gets Infiltrate like normal Stealth Suits, but if it does, then that is quite a solid addition to its mobility toolkit.
2 – Survivability — At only T5, 4W, and a 3+ save, at first glance it looks like a pretty fragile MC. However, with potential access to Stealth, Shrouded, and even additional cover enhancement rules/Wargear, I suspect that the Ghostkeel will be able to get a 3+ or even 2+ cover save a lot of the time while employed by a skilled player. Combine this with Wargear for FNP and suddenly you have a much tougher unit, especially since it can be taken in teams of up to 3 Battlesuits. If it gets a 2+ cover save and FNP from war gear, then statistically it would take a BS4 Plasma Gun 64 shots to kill a Ghostkeel outright. Similarly, BS4 Grav Cannon/Amps would take about 60 shots to completely kill a single XV95, provided it has access to a 2+ cover save). Add in drones for additional wound mitigation and, needless to say, that is a very solid ability to act as fire magnet from the rest of your army.
3 – Firepower — With basically a Small Blast Fusion Blaster and a TLed Flamer stock, where I think the Ghostkeel really shines is upgrading to a 6 shot S7 AP4 Ion Weapon and a TLed Fusion Blaster. With these two weapons, the Battlesuit’s built in survivability, the option to take 3 models per team, and Markerlight support, you have the ability to create a very solid transport hunter unit which can hunt effectively in the enemy backfield for all those solid side armor/rear armor shots. Alternately, you can max out melta weapons and hunt Terminators, Land Raiders, and enemy HQ types with a solid degree of efficiency.
4 – Close Combat — While obviously not great in this role (with only T5, 3+ save, and poor Tau CC stats), it still is a MC, so that means AP2 hits at initiative, meaning you have to be careful when you assault a Ghostkeel (or a full 3 Suit Team of them!). It also has the Smash option to get a S10 hit against vehicles if required after you shoot them up with melta weapons.
Overall, we will see where it fits into the overall Tau “order of battle” within the new codex, but as an Elites choice I expect the Ghostkeel to be solidly competitive both internally compared to other Tau units and externally vis-à-vis enemy units on the tabletop.