Q: So this is what I understand, and please correct me if it's off: it seems to me that when the allocator fee is included, the exchange rate need not be 1:1 for hybrid living on different chains.  It's (1+fee1 : 1+fee2), which amounts to a floating exchange rate set by market forces.  This makes economic sens as a way liquidity can be provided, but also means that the hybrid on each chain are effectively different currencies, in the sense that they would be priced separately on any std exchange (e.g. Poloniex), and there's no reason their prices would need to be close to the same as one another.
I see that this arbitrage could exist (and hence correct for) price mismatches between Hybrid(XCP) vs Hybrid(ETH) as existing via IOC swap vs as implied by those prices and the ETH:XCP prices on exchanges.  What I don't see is that this forces the price of Hybrid(XCP) : Hybrid(ETH) to stay close to 1.  I.e. as long as prices are consistent (but possibly different from 1) then no arbitrage will be possible. The price would have to be close to 1 if the IoC coinswap could guarantee liquidity at that price, but again I dont see how it could do that without market-based fees, which effectively is equivalent to a floating price, not a fixed price of 1.

There is a slight float. Our system creates the orderbooks automatically, and keeps prices as close to 1:1 as possible, and limits the possibility to go too far beyond that. For that we are using a covariance algorithm to predict differences in the portfolio of HYBRID's users are holding. We will be going towards using Nash's equilibrium with our mathematician to put a more advanced prediction model into the balancing algorithm.

Q: Hence this is a potential source of inflation for hybrid holders, yes?  I.e. if you increase the hybrid supply to add a new coin and make that hybrid exchangeable wrt the existing hybrid.

Without funding the new emission it is an inflation. We will not add non-funded emissions to HYBRID, however, so technically it is not an inflation in that it decreases vested token value.

Q: WIthout issuing new tokens, this would be inflation-free

That is correct.

Q: My question was aiming at something different.  Im not concerned with the gap between the max of 900k tokens sold per chain and the remaining 100k, which are to be issued over the next few years.  I'm concerned with e.g. if e.g. only 9k tokens are sold for e.g. NXT.  Then are you only going to issue 9k (10k) hybrid on NXT, or will you issue 900k (1M), in which case how will those extra tokens be distributed?  That's a major inflationary concern at the moment, since only ~215k hybrid have been sold out of a possible 6.3M (7M)

A proper concern, and something we are also looking at. We'd like to see the amounts of HYBRID on different chains to be synchronous as planned originally, i.e. 1M per chain. In this first emission of HYBRID, it could be that not all tokens are sold, and for this situation we are thinking of distributing the rest of the tokens among current HYBRID holders, so everyone receives the adequate percentage belonging to his/her participation in the marketcap the crowdfund has created.