The current SpaceX Falcon 9 boosters that have been recovered were only designed to be reused 2-3 times but the new SpaceX Falcon 9 block 5 are expected to last for ten reuses. SpaceX has about 6 recovered boosters which will be reused. Most will be reused and not recovered in the next several launches.
SpaceX is counting on Block 5 to succeed with increased reusability and for faster relaunching. If any design or manufacturing flaws are discovered in the first several Block 5 Falcon 9s, or if Block 5 is less reusable than SpaceX then SpaceX could have delays in its launch schedule.
The first Block 5 Falcon 9 first stage is on the test stand at their McGregor, Texas test facility.
The maiden flight is planned for April 2018, with the Bangabandhu-1 satellite.
SpaceX Block 5 improvements:
Alterations are focused on increasing the speed of production and efficiency of re-usability. SpaceX aims to fly each Block 5 booster ten times with only inspections in between, and up to 100 times with refurbishment
For increased payload:
7–8% more thrust by uprating the engines;
An improved flight control system for an optimized angle of attack on the descent, lowering landing fuel requirements.
For reusability endurance:
A reusable heat shield protecting the engines and plumbing at the base of the rocket;
More temperature-resistant titanium casted grid fins;
A thermal protection coating on the first stage to limit reentry heating damage;
Redesigned and requalified valves for higher levels and much longer duration.
For rapid reusability:
A set of black retractable landing legs for rapid recovery and shipping.
Block 5 is planned to launch astronauts for the first time in late 2018. NASA requires seven flights before the vehicle can be certified for human spaceflight.