The core actually had older ablative grid fins made of aluminium so no great loss there[0].
Your typical mechanical engineer fresh out of school has incredibly limited experience when it comes to things that are not stupid-proof to work with (engineering programs have other priorities). They then go on to build specialized knowledge in various subjects and usually more on the design side, not the execution side. Of course someone who designs plastic molds or simulated impeller designs all day is going to create a black box around things that aren't their specialty. You don't care about how the impeller or mold is made other than knowing that it can be made, what its material properties are and knowing that actually making it involves a bunch of details you don't know so you offload it to a 3rd parts (for the same reasons someone else is having you design the impeller or the mold).
A bunch of engineers and otherwise smart people on the internet saying that titanium is like computer programmers saying residential electrical is complicated or web devs complaining about bash. It really doesn't mean much but people who have no experience with this things tend to think the people who only have a shred know what they're talking about.
It's not difficult. Most other people just know they don't know how to do it and that they don't know what they'd need to know to go about learning how.
The mental image of it leaking so much fuel on the ground such that it needed immediate refuelling is a myth propagated extensively on the internet.
I had a quick search and found the KC135 chap who says the refuelling was needed due to leaks, but without being rude to him I'm not sure he's really a qualified source for that information. It sounds more to me like 2+2=5.
I'm procrastinating so lets do some napkin maths, the claim is
1) a significant amount of fuel is leaking out of the expansion gaps,
2) climbing up to 25,000 ft at 300 knots would heat the airframe enough to seal those gaps,
3) there would still be sufficient expansion room to allow for travelling at M3.2
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Ignoring that no engineer would be happy with 1.
For 2...Total Air Temp = Static Air Temp + Ram Rise. At 25,000 ft the static air temperature is about -35 C. Ram rise for a true airspeed of 300 kts:
RamRise = V^2 / 87^2 = 300^2 / 87^2 = 12 degrees.
So skin temperature at typical refuelling altitude would be -23 C
Titanium has an expansion coefficient of 9E-69 meters per meter-kelvin. So approximating rather grossly, assuming a s tarting temperature of 20 C over the 33 m length of the plane there would be a contraction of about 1 cm.
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And for 3:
The aircraft then accelerates up to 1900 knots. RamRise = 1900^2 / 87^2 = 470 degrees
Static air temp at over 60000 ft is roughly -55 C. So skin temperature would be 420 C. So assuming the same length and starting temp, the plane would expand by around 11 cm
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So to summarise: According to the claims, at ground level and temperature the expansion gaps were large enough to significantly leak fuel. After take-off the aircraft needs to be refuelled immediately. Assuming this is done so (i.e. take-off, climb to 20,000, refuel) then the skin temperature is lower than ground level, and the expansion gaps should have grown ever so slightly. The aircraft then climbs up to its M3.2 cruise point and everything expands significantly "as designed" and the gaps disappear.
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Perhaps the anecdote we'll see on the internet now is that the SR-71 had to take off and go supersonic to rapidly heat up the skin before briefly decelerating to refuel, but the refuel had to be done super fast to stop the skin cooling down too far...
From your source: "Fuselage panels were manufactured to fit only loosely on the ground. Proper alignment was achieved as the airframe heated up and expanded several inches.[30] Because of this, and the lack of a fuel-sealing system that could handle the airframe's expansion at extreme temperatures, the aircraft leaked JP-7 fuel on the ground prior to takeoff."
If you dig past the internet comments and read some of the "primary source" books, the picture of the leaks is very different. I can't remember the exact book I read it in, but the author states there was a tank sealant, and it lasted around 50 hours (I think), before it needed to be replaced.
This is somewhat backed up by the Jenkins book [1] which talks about the time consuming process of replacing sealant, and the Graham book [0] that is the source for the Wikipedia claims on expansion. It talks of different sealants used, and how leaks were precisely noted and collected in _shallow_ drip trays.
[0] https://books.google.co.uk/books?id=dX5cCgAAQBAJ&pg=PA129&dq...
[1] https://books.google.co.uk/books?id=lEpWE748QUsC&q=sr71+seal...
They are however interested in recovering the grid fins on the side boosters, which were redesigned to accommodate for the nose cones now sitting on top of them.
But yeah, that's just a question from my mind. This launch was amazing, the future in the making right here.
https://www.reddit.com/r/spacex/wiki/cores#wiki_.5Bfh.5D_b10...
Almost (if not) all missions include changes of some kind; the manufacturing blocks each have significant, incompatible differences in parts.
Upgrading the grid fins would be a minor version change, modifying the engine to increase its throttle depth a major one. I don't know, but it seems like there would need to be significant re-tooling for each new block, and many parts would be incompatible with previous blocks.
Perhaps some piece of metal is showing more fatigue than they'd like to see, or a wire had damage to the insulation from a vibration. I'm sure that's the sort of thing they'll be looking at.