As someone who has worked on a VM, I couldn't disagree more. It can take years to hash out things as simple as ideally performing primitives for a target architecture, and then things change.
Add to that the complexity of optimizing compilers, specification of byte code formats and a consistent virtual machine memory model that can be relied upon across architectures, and the art and science of highly concurrent garbage collectors, and your "no big deal" is a load of hogwash.
Hotspot alone is nearly 20 years of big deal.
> A team made of relatively small number of people (high quality, but low quantity) can and do maintain VMs ...
The number of people doesn't matter in this equation; your small team of (expensive, rare, high quality people) can't build a world-class VM in a day. Or a month. Or a year. Maybe in 5 or 10 years, just ask Microsoft.
> ... like HotSpot and V8. LuaJIT is maintained by a single person.
LuaJIT's said "single person" has been working on it for what, 10 years? It's an extremely impressive implementation and I don't want to bag on it, but even still, it lags in certain areas, eg, its GC implementation isn't up to par with the state of the art.
The author's skillset is extremely rare, and LuaJIT itself is an anomaly in the field. Using such a one-off example doesn't really hold water to prove that it's ideal for a company to internalize maintaining a VM for their own custom language built on top of PHP.
On the other hand, I maintain it still is no big deal compared to rewriting Facebook. I also maintain while skillset is rare, Facebook apparently had no trouble so far and will have no trouble in the future finding (I remind you, small number of) people to work on VM. I also remind you Facebook has been working on alternative PHP implementation for 6 years now, 2 years in private(2008~2010) and 4 years in public(2010~2014). It has been profitable for them for 6 years, will be profitable in the future, and profitability does not need "sharing maintenance load with the wider industry". They can maintain it fine thank you very much. Because, in the end, VM is no big deal.
They're also continuing to propagate an outwardly facing engineering culture that will make it even harder to hire people to help dig them out of the PHP hole -- perpetuating this further.
Your argument is simply another take on survivor bias fallacy.
> I get paid to do these stuffs, and I am on my third VM/PL project now ... Because, in the end, VM is no big deal.
You keep saying that, and yet, there keep being so few high quality VMs.
It's possible that they could eventually get a total rewrite to give a better return, but frankly I don't think you have any idea of the enormity of trying to convert a multi-million line production platform from one language to another.
In any case, one does not preclude the other. Arguably, many of the changes they have made, such as gradual typing, and their ability to now slowly introduce other changes without breaking their existing codebase, means they have a platform for slowly firming up their codebase and migrate it towards a position where a full rewrite (should they decide to do one in the future) could be made substantially less painful.
