Two things immediately spring to mind:

1. If it's valued in euro then the face value has to be in euro.  You can't sell all 100k at same BTC price as if they don't sell quickly and the exchange-rate moves it would be impossible for you to honour the contract to investors who bought at different exchange-rates.

2.  You can't issue a bond which is only secured against the assets purchased with capital raised from the bonds:
a)  That would necessitate you keeping seperate accounts in respect of the bonds - with all purchases recorded as being purchased with bond-capital or purchased with other capital.
b)  It's grossly unfair to purchasers of the bonds.  They take all losses associated with the bonds but have profits capped at 22% growth expressed in euros.

Bonds are issued by the company and secured against ALL its assets.  Bond-holders have senior claim over equity holders.

EDIT: It occurs to me that when you say "based on EUR/BTC value at time of issue" you may mean at time dividend is paid rather than at time the bonds were issued.  In that case my point 1 doesn't apply - though it then makes no sense as the interest would be based on BTC face value anyway (just with two currency conversions to get back to where you started from).